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Document and Entity Information	9 Months Ended
Document and Entity Information	Sep. 30, 2018
Document And Entity Information [Abstract]
Document Type	S-1
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Trading Symbol	XERS
Entity Registrant Name	XERIS PHARMACEUTICALS INC
Entity Central Index Key	0001346302
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 75,745	$ 42,045	$ 32,269
Short-term Investments	55,296	0
Accounts receivable, net	1,731	1,199	101
Prepaid expenses and other current assets	2,898	809	804
Total current assets	135,670	44,053	33,174
Property and equipment, net	1,826	788	312
Other assets	95	157	47
Total assets	137,591	44,998	33,533
Current Liabilities
Accounts payable	622	1,976	1,315
Accrued expenses	6,260	2,557	902
Warrant liabilities	1,042	93	47
Deferred grant award	284	234	263
Total current liabilities	8,208	4,860	2,527
Long-term debt, net of deferred costs	31,642	0
Deferred rent-long term	2,621	90	42
Total liabilities	42,471	4,950	2,569
Commitments and contingencies (Note 8)
Convertible preferred stock
Series A Convertible Preferred Stock-par value	0	1,945	1,945
Series B Convertible Preferred Stock-par value	0	18,536	18,536
Series C Convertible Preferred Stock-par value	0	77,397	42,417
Total convertible preferred stock	0	97,878	62,898
Stockholders' Deficit
Preferred stock-par value	0	0
Common stock-par value	2	1	1
Additional paid in capital	195,422	2,754	2,096
Accumulated deficit	(100,246)	(60,585)	(34,031)
Accumulated other comprehensive loss	(58)	0
Total stockholders' equity (deficit)	95,120	(57,830)	(31,934)
Total liabilities, convertible preferred stock and stockholders' deficit	$ 137,591	$ 44,998	$ 33,533

Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Preferred Stock, Par Value Per Share	$ 0.0001
Preferred Stock, Shares Authorized	10,000,000
Preferred Stock, Shares Issued	0
Preferred Stock, Shares Outstanding	0
Common Shares, Par Value Per Share	$ 0.0001	$ 0.0001	$ 0.0001
Common Stock, Shares Authorized	150,000,000	30,450,994	21,247,980
Common Shares, Shares, Issued	20,755,666	2,159,068	1,927,237
Common Stock, Shares, Outstanding	20,755,666	2,159,068	1,927,237
Preferred Stock, Series A [Member]
Preferred Stock, Par Value Per Share		$ 0.0001	$ 0.0001
Preferred Stock, Shares Authorized		1,864,797	1,864,797
Preferred Stock, Shares Issued		1,843,965	1,843,965
Preferred Stock, Shares Outstanding		1,843,965	1,843,965
Preferred Stock, Liquidation Preference, Value		$ 1,881
Preferred Stock, Series B [Member]
Preferred Stock, Par Value Per Share		$ 0.0001	$ 0.0001
Preferred Stock, Shares Authorized		5,732,338	5,732,338
Preferred Stock, Shares Issued		5,696,834	5,696,834
Preferred Stock, Shares Outstanding		5,696,834	5,696,834
Preferred Stock, Liquidation Preference, Value		$ 18,908
Preferred Stock, Series C [Member]
Preferred Stock, Par Value Per Share		$ 0.0001	$ 0.0001
Preferred Stock, Shares Authorized		14,353,859	7,973,845
Preferred Stock, Shares Issued		12,834,912	7,177,398
Preferred Stock, Shares Outstanding		12,834,912	7,177,398
Preferred Stock, Liquidation Preference, Value		$ 80,481

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Grant income	$ 1,611	$ 1,073	$ 1,540	$ 1,022
Service revenue	53	16	16	53
Cost of revenue	42	4	4	8
Gross profit	1,622	1,085	1,552	1,067
Operating expenses
Research and development	28,264	13,588	20,166	10,238
General and administrative	12,388	4,917	8,015	4,060
Expense from operations	40,652	18,505	28,181	14,298
Loss from operations	(39,030)	(17,420)	(26,629)	(13,231)
Other income (expense)
Interest income	796	45	124	5
Interest expense	(1,490)	(1)	(2)	(2)
Change in fair value of warrants	63	(32)	(46)	24
Other expense			(1)	(5)
Total other income	(631)	12	75	22
Net loss	$ (39,661)	$ (17,408)	$ (26,554)	$ (13,209)
Net loss per share-basic and diluted	$ (4.36)	$ (8.63)	$ (13.09)	$ (7.17)
Other comprehensive loss, net of tax
Unrealized losses on short-term investments	$ (58)	$ 0
Comprehensive loss	$ (39,719)	$ (17,408)
Weighted average shares outstanding, basic and diluted	9,104,491	2,016,112	2,028,224	1,842,416
Pro Forma [Member]
Other income (expense)
Net loss per share-basic and diluted			$ (2.34)
Other comprehensive loss, net of tax
Weighted average shares outstanding, basic and diluted			11,385,655

Condensed Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Series C Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Shareholder Notes Receivable [Member]
Beginning Balance at Dec. 31, 2015	$ (19,377)				$ 1	$ 1,534		$ (20,822)	$ (90)
Temporary equity, Beginning Balance at Dec. 31, 2015		$ 1,787	$ 18,536	$ 38,569
Beginning Balance, shares at Dec. 31, 2015					1,815,651
Temporary equity, Beginning Balance, shares at Dec. 31, 2015		1,796,174	5,696,834	6,539,490
Net loss	(13,209)							(13,209)
Exercise of Series A Warrants		$ 49
Exercise of Series A Warrants, Shares		47,791
Fair market value of preferred stock warrants charged to Series A Preferred stock		$ 109
Issuance of Series C Preferred Stock, net of cost				$ 3,848
Issuance of Stock, shares				637,908
Repayments on shareholder notes	17								17
Allowance on shareholder notes	73								$ 73
Exercise and vesting of stock based awards	22					22
Exercise and vesting of stock based awards, Shares					111,586
Stock based compensation	540					540
Temporary equity, Ending Balance at Dec. 31, 2016		$ 1,945	$ 18,536	$ 42,417
Temporary equity, Ending Balance, shares at Dec. 31, 2016		1,843,965	5,696,834	7,177,398
Ending Balance at Dec. 31, 2016	(31,934)				$ 1	2,096		(34,031)
Ending Balance, shares at Dec. 31, 2016					1,927,237
Net loss	(26,554)							(26,554)
Issuance of Series C Preferred Stock, net of cost				$ 34,980
Issuance of Stock, shares				5,657,514
Exercise and vesting of stock based awards	159					159
Exercise and vesting of stock based awards, Shares					231,831
Stock based compensation	499					499
Temporary equity, Ending Balance at Dec. 31, 2017		$ 1,945	$ 18,536	$ 77,397
Temporary equity, Ending Balance, shares at Dec. 31, 2017		1,843,965	5,696,834	12,834,912
Ending Balance at Dec. 31, 2017	(57,830)				$ 1	2,754		(60,585)
Ending Balance, shares at Dec. 31, 2017					2,159,068
Net loss	(39,661)							(39,661)
Issuance of Initial Public Offering	88,952					88,952
Issuance of Series C Preferred Stock, net of cost				$ 4,414
Issuance of Stock, shares				707,680	6,555,000
Exercise and vesting of stock based awards	275					275
Exercise and vesting of stock based awards, Shares					204,525
Conversion of convertible preferred stock into common stock	102,293	$ (1,945)	$ (18,536)	$ (81,811)	$ 1	102,292
Conversion of convertible preferred stock into common stock, Shares		(1,843,965)	(5,696,834)	(13,542,592)	11,837,073
Stock based compensation	1,149					1,149
Comprehensive loss	(58)						$ (58)
Ending Balance at Sep. 30, 2018	$ 95,120				$ 2	$ 195,422	$ (58)	$ (100,246)
Ending Balance, shares at Sep. 30, 2018					20,755,666

Condensed Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Series C Convertible Preferred Stock [Member]
Issuance of Series C Preferred Stock, cost	$ 24	$ 395	$ 152

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
Condensed Statements of Cash Flows - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net loss	$ (39,661)	$ (17,408)	$ (26,554)	$ (13,209)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	146	123	177	116
Amortization of debt issuance costs	312	0
Impairment of fixed assets			48	0
Stock-based compensation	1,149	351	499	540
Change in fair value of warrants	(63)	32	46	(24)
Allowance for shareholder note receivable				73
Changes in operating assets and liabilities
Accounts receivable	(532)	(635)	(1,098)	204
Prepaid expenses and other current assets	(2,089)	262	(5)	(294)
Other assets	62	(55)	(111)	1
Accounts payable	(1,354)	299	661	(2,909)
Accrued expenses	3,790	1,473	1,703	(552)
Deferred grant award	50	(25)	(29)	(33)
Deferred rent	246	20
Net cash used in operating activities	(37,944)	(15,563)	(24,663)	(16,087)
Cash flows from investing activities
Purchases of property and equipment	(1,260)	(464)	(700)	(35)
Purchases of short-term investments	(55,278)	0
Net cash used in investing activities	(56,538)	(464)	(700)	(35)
Cash flows from financing activities
Proceeds from Initial Public Offering	98,325	0	30,000
Payments for Initial Public Offering Costs	(9,373)	0
Proceeds from sale of Series C Preferred Stock	4,438	30,050	35,475	4,000
Payments of Series C Preferred Stock offering costs	(24)	(434)	(495)	(152)
Proceeds from issuance of long-term debt	35,000	0
Proceeds from exercise of preferred stock warrants				49
Payments for debt issuance costs	(333)	0
Proceeds from shareholder notes receivable				17
Repayments of capital lease				(32)
Proceeds from exercise of stock awards	149	56	159	22
Net cash provided by financing activities	128,182	29,672	35,139	3,904
Increase (decrease) in cash and cash equivalents	33,700	13,645	9,776	(12,218)
Cash and cash equivalents, beginning of year	42,045	32,269	32,269	44,487
Cash and cash equivalents, end of year	75,745	45,914	42,045	32,269
Supplemental schedule of cash flow information
Income taxes paid			0	0
Cash paid for interest	1,031	1	$ 2	2
Supplemental schedule of non-cash investing and financing activities
Change in fair market value of expired warrants				$ 109
Allocation of debt costs to warrants	1,012	0
Accrued debt issuance costs	2,325	0
Vesting of early exercised awards	$ 127	$ 0

Organization and Nature of the Business	9 Months Ended	12 Months Ended
Organization and Nature of the Business	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Nature of the Business	Note 1. Organization and Nature of the Business *Nature of business* Xeris Pharmaceuticals, Inc. (“Xeris” or the “Company”) is a specialty pharmaceutical company that was incorporated in Delaware in 2005. Xeris is dedicated to the development of ready-to-use injectable and infusible drug formulations that address important unmet medical needs, are easier to use by patients, caregivers and health practitioners, and reduce costs for payors and the healthcare system. *Basis of presentation* The financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Since its inception, the Company has devoted substantially all of its efforts to research and development, regulatory and technical activities. The Company has financed its operations through the issuance of common stock in its June 2018 initial public offering (“IPO”), issuance of convertible preferred stock and other equity instruments, issuance of debt and grant funding from the National Institutes of Health (“NIH”) and other philanthropic organizations. The Company has not generated any revenue from product sales. The Company has incurred operating losses since inception and has an accumulated deficit of $100.2 million as of September 30, 2018. The Company expects to continue to incur net losses for the next several years. Based on the Company’s current operating plans and existing working capital at September 30, 2018, cash resources are sufficient to sustain operations and capital expenditure requirements for at least the next 12 months. The Company is subject to a number of risks similar to other specialty pharmaceutical companies, including, but not limited to, successful development and commercialization of its drug candidates, the development of new technological innovations by its competitors, protection of intellectual property and market acceptance of the Company’s products.	Note 1. Organization and Nature of the Business *Nature of business* Xeris Pharmaceuticals, Inc. (“Xeris” or the “Company”) is a specialty pharmaceutical company that was incorporated in Delaware in 2005. Xeris is dedicated to the development of ready-to-use injectable and infusible drug formulations to address important unmet medical needs and that are easier to use by patients, caregivers and health practitioners, and reduce costs for payors and the healthcare system. *Basis of presentation* The financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Since its inception, the Company has devoted substantially all of its efforts to research and development, regulatory and technical activities. The Company has financed its operation through the issuance of convertible preferred stock and other equity instruments and grants from the National Institutes of Health and other philanthropic organizations. The Company has not generated any revenue from product sales. The Company has incurred operating losses since inception and had an accumulated deficit of $34.0 million and $60.6 million as of December 31, 2016 and 2017, respectively. The Company expects to continue to incur net losses for the next several years and is highly dependent on its ability to find additional sources of funding in the form of debt and/or equity financing and grant awards to fund its operations. The Company’s ability to fund its planned clinical operations, including completion of its planned trials, and commercialization of its product candidates is expected to depend on the amount and timing of cash receipts from financing transactions and grant awards. Adequate additional funding may not be available to the Company on acceptable terms or at all. The failure to raise funds as and when needed could have a negative impact on the Company’s financial condition and ability to pursue its business strategies. Based on the Company’s current operating plans, existing working capital at December 31, 2017 combined with the $35.0 million in expected proceeds from the Loan and Security Agreement (the “Loan Agreement”) with Oxford Finance LLC (Oxford) and Silicon Valley Bank (SVB) (collectively, the “Lenders”) and $4.4 million in Series C Convertible Preferred Stock sold in February 2018, cash is sufficient to sustain operations beyond March 21, 2019. If additional funding is not secured when required, the Company may need to delay or curtail its operations until such funding is received. The Company is subject to a number of risks similar to other specialty pharmaceutical companies, including, but not limited to, successful development and commercialization of its drug candidates, raising additional capital, the development of new technological innovations by its competitors, protection of intellectual property and market acceptance of the Company’s products.

Summary of Significant Accounting Policies

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2. Summary of Significant Accounting Policies

The accompanying unaudited interim financial statements have been prepared in conformity with GAAP. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).

In the opinion of management, the accompanying unaudited interim financial statements include all normal and recurring adjustments (which consist primarily of accruals and estimates that impact the financial statements) considered necessary to present fairly the Company’s financial position as of September 30, 2018 and its results of operations and cash flows for the nine months ended September 30, 2018 and 2017. Operating results for the nine month periods ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018. The unaudited interim financial statements, presented herein, do not contain the required disclosures under GAAP for annual financial statements. The accompanying unaudited interim financial statements should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2017 included in the prospectus (Registration No. 333-225191) filed pursuant to Rule 424(b) on June 21, 2018 with the U.S. Securities and Exchange Commission.

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, contingent liabilities and expenses included in the financial statements and accompanying notes. Actual results could differ from those estimates.

Impacts of the Tax Cuts and Jobs Act

On December 22, 2017, the Tax Cuts and Jobs Act (H.R. 1) (the “Tax Act”) was signed into law. The Tax Act contains significant changes to corporate taxation, including (i) the reduction of the corporate income tax rate to 21%, (ii) the acceleration of expensing for certain business assets, (iii) the one-time transition tax related to the transition of U.S. international tax from a worldwide tax system to a territorial tax system, (iv) the repeal of the domestic production deduction, (v) additional limitations on the deductibility of interest expense, and (vi) expanded limitations on executive compensation. The key impacts of the Tax Act on the Company’s financial statements for the year ended December 31, 2017 were the re-measurement of deferred tax balances to the new corporate tax rate. While the Company has not yet completed the assessment of the effects of the Tax Act, the Company was able to determine reasonable estimates for the impact of the key items specified above and thus it reported provisional amounts for these items. In accordance with Staff Accounting Bulletin No. 118 (“SAB 118”), the Company provides additional disclosures related to these provisional amounts. In order to calculate the effects of the new corporate tax rate on its deferred tax balances, ASC 740 “Income Taxes” (“ASC 740”) required the re-measurement of the Company’s deferred tax balances as of the enactment date of the Tax Act, based on the rates at which the balances were expected to reverse in the future. The provisional amount determined, and recorded as of December 31, 2017, for the re-measurement of its deferred tax balances resulted in a net reduction in deferred tax assets of $7,478,000 and a corresponding reduction in the valuation allowance of $7,478,000.

The aforementioned provisional amounts related to the deferred tax balances are based on information available at this time and may change due to a variety of factors, including, among others, (i) anticipated guidance from the U.S. Department of Treasury about implementing the Tax Act, (ii) potential additional guidance from the U.S. Securities and Exchange Commission or the FASB related to the Tax Act and (iii) management’s further assessment of the Tax Act and related regulatory guidance. The Company is not complete in its assessment of the impact of the Tax Act on its business and financial statements. The effective date of most of the provisions of the Tax Act applies to the Company’s tax year beginning January 1, 2018. The Company will continue the assessment of the impact of the Tax Act on its business and financial statements throughout the one-year measurement period as provided by SAB 118.

Debt issuance costs

Long-term debt is accounted for at amortized cost. Debt issuance costs incurred in connection with financing arrangements are amortized to interest expense over the life of the respective financing arrangement using the effective interest method. Debt issuance costs, net of related amortization, are deducted from the carrying value of the related debt.

Equity financing costs

The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated, at which time such costs are recorded in the additional paid in capital line on the balance sheet against the gross proceeds of the equity financings. As of September 30, 2018, the Company incurred $9.4 million in costs associated with the IPO.

Fair value of financial instruments

Fair value is the price that could be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value determination in accordance with applicable accounting guidance requires that a number of significant judgments be made. Additionally, fair value is used on a non-recurring basis to evaluate assets for impairment or as required for disclosure purposes by applicable accounting guidance on disclosures about fair value of financial instruments. Depending on the nature of the assets and liabilities, various valuation techniques and assumptions are used when estimating fair value. The carrying amounts of certain of the Company’s financial instruments, including cash and cash equivalents, accounts receivable, prepaid expenses and other current assets, and accounts payable, are shown at cost, which approximates fair value due to the short-term nature of these instruments. The debt outstanding under the Loan and Security Agreement approximates fair value due to the variable interest rate on the debt. Items measured at fair value on a recurring basis include the Company’s short-term investments and warrants.

Net loss per common share

Basic and diluted net loss per common share is determined by dividing net loss applicable to common stockholders by the weighted average common shares outstanding during the period. For all periods presented, the outstanding shares of the preferred stock, warrants, and stock awards have been excluded from the calculation because their effects would be anti-dilutive. Therefore, the weighted average common shares outstanding used to calculate both basic and diluted loss per common share are the same.

The following potentially dilutive securities (shown below in common stock equivalent shares) were excluded from the computation of diluted weighted average common shares outstanding due to their anti-dilutive effect:


	SEPTEMBER 30,
	2017		2018
Convertible preferred stock		10,954,012		—
Warrants		19,931		113,943
Vested and unvested stock options		1,902,997		2,753,208

		12,876,940		2,867,151

Recent accounting pronouncements

In March 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share Based Payment Accounting (“ASU 2016-09”), as part of the FASB simplification initiative. The new standard provides for changes to accounting for stock compensation including 1) excess tax benefits and tax deficiencies related to share-based payment awards being recognized as income tax expense in the reporting period in which they occur; 2) excess tax benefits being classified as an operating activity in the statement of cash flow; 3) the option to elect to estimate forfeitures or account for them when they occur; and 4) increased tax withholding requirements threshold to qualify for equity classification. ASU 2016-09 is effective for public companies with annual periods and interim periods beginning after December 15, 2016. Early adoption is permitted. The Company adopted this standard on January 1, 2018, and it did not have an impact on the financial statements.

Note 2. Summary of Significant Accounting Policies

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and contingent liabilities and expenses included in the financial statements and accompanying notes. Actual results could differ from those estimates.

Grant Income

The Company has received several grants from the National Institutes of Health and other philanthropic organizations for certain research and development projects the Company is currently performing. Grant income is recognized when these research and development activities are performed, and the Company has met criteria for reimbursement per the grant agreements. The Company also has grants where cash is received upfront. The Company defers these awards until the research and development expenses are incurred.

Revenue

The Company recognizes revenue when persuasive evidence of an arrangement exists, the related services have been performed, the price is fixed and determinable and collectability is reasonably assured. The Company generates revenue through the performance of research and development activities on behalf of others.

Research and development costs

Research and development costs are expensed as incurred. Research and development costs include salaries, stock compensation and other personnel-related costs, consulting fees, fees paid for contract research services, laboratory equipment and facilities costs, and other external costs.

Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are received or the services are performed.

Stock-based compensation

The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees, including grants of employee stock options, to be recognized in the statements of operations based on their grant date fair values. The Company estimates the grant date fair value of each option award using the Black-Scholes option-pricing model. The use of the Black-Scholes option-pricing model requires management to make assumptions with respect to the expected term of the option, the expected volatility of the common stock consistent with the expected life of the option, risk-free interest rates and expected dividend yields of the common stock. The Company recognizes stock-based compensation expense, net of estimated forfeitures, equal to the grant date fair value of stock options on a straight-line basis over the requisite service period. Restricted stock awards are valued based on the fair market value of the Company’s common stock on the date they were granted. Restricted stock that vests and stock options that are authorized are issued out of authorized available shares.

The Company accounts for stock-based awards issued to non-employees by recognizing compensation expense based on the fair value of such awards when the services are completed over the vesting period of the award.

Income Taxes

Income taxes are recorded in accordance with ASC 740, Accounting for Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. The Company determines its deferred tax assets and liabilities based on differences between financial reporting and tax bases of assets and liabilities, which are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are provided if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2017, the Company does not have any significant uncertain tax positions.

Cash and cash equivalents

Cash and cash equivalents include demand deposits with financial institutions and liquid investments with original maturities of three months or less.

Concentrations of risk

The Company has no off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.

The Company is dependent on several key suppliers and third-party manufacturers. A failure or disruption by one of the Company’s key suppliers or third-party manufacturers may have a material impact to its planned operations.

Prepaid expenses and other current assets

Prepaid expenses and other current assets include prepaid expenses for general business purposes, which are stated at cost and are amortized on a straight-line basis over the related period of benefit. Prepaid expenses also include supplies and materials used in several research projects. These supplies are expensed as they are consumed.

Property and equipment

Property and equipment are carried at cost less accumulated depreciation. Depreciation is calculated utilizing the straight-line method over the estimated useful lives of the respective assets:


Lab equipment			5 years
Computer equipment			5 years
Leasehold improvements			Lesser of useful life or lease term
Software			3-5 years
Furniture and fixtures			5 years
Office equipment			5 years

Costs of major additions and betterments are capitalized; maintenance and repairs, which do not improve or extend the life of the respective assets, are charged to expense as incurred. Upon retirement or sale, the cost of the disposed asset and the related accumulated depreciation are removed from the accounts and the resulting gain or loss is recognized.

Impairment of long-lived assets

The Company periodically evaluates its long-lived assets for potential impairment in accordance with ASC Topic 360, Property, Plant and Equipment. Potential impairment is assessed when there is evidence that events or changes in circumstances indicate that the carrying amount of an asset may not be recovered. Recoverability of these assets is assessed based on undiscounted expected future cash flows from the assets, considering a number of factors, including past operating results, budgets and economic projections, market trends and product development cycles. If impairments are identified, assets are written down to their estimated fair value. The Company recognized impairment charges of $0 and $48,000 for the years ended December 31, 2016 and 2017, respectively. The impairment charge in 2017 was related to equipment that is no longer used in the Company’s manufacturing of the Gvoke HypoPen due to process and formulation improvements.

Deferred rent

Certain of the Company’s lease agreements provide for scheduled rent increases during the lease term and for rental payments commencing at a date after the initial occupancy date. Provisions are made for the excess of operating lease rentals, computed on a straight-line basis throughout the lease term, over cash rentals paid.

Preferred stock

The Company’s Series A, B and C Convertible Preferred Stock (collectively known as “Preferred Stock”) allows the holders to redeem their shares upon a change in control in the Company. As a result, the Company classifies its Preferred Stock as mezzanine equity. The Company charges specific incremental issuance costs incurred in the offering of Preferred Stock against the gross proceeds of the Preferred Stock.

Warrants

Warrants for the Company’s convertible preferred stock are liability classified as they represent a financial instrument for a share of convertible preferred stock. The warrants are revalued each reporting period with the change in fair value recorded in the accompanying statements of operations until the warrants are exercised, expire, reclassified to permanent equity, or otherwise settled.

Fair value of financial instruments

Segments

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker (“CODM”) in making decisions regarding resource allocation and assessing performance. The Company’s chief executive officer uses summary financial information in determining how to allocate resources and assess performance. The Company has determined that it operates in one segment and all of the Company’s assets are located in the United States.

Net loss per share

Basic and diluted net loss per common share is determined by dividing net loss applicable to common stockholders by the weighted-average common shares during the period. For all periods presented, the outstanding shares of the Preferred Stock, preferred stock warrants, and stock awards have been excluded from the calculation because their effects would be anti-dilutive. Therefore the weighted-average shares used to calculate both basic and diluted loss per share are the same.

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2016 and 2017, as they would be antidilutive:


	YEARS ENDED DECEMBER 31,
	2016		2017
Convertible preferred stock		8,263,377		11,439,752
Warrants		19,931		19,931
Vested and unvested stock options		508,328		1,979,306

		8,791,636		13,438,989

Amounts in the table above reflect the common stock equivalents of the noted instruments.

The unaudited pro forma net loss per common share is computed using the weighted-average number of common shares outstanding and assumes the issuance of 11,459,683 shares of common stock issued to the holders of the Company’s Preferred Stock and preferred stock warrants upon an initial public offering as if such conversion had occurred at the beginning of the period presented or the date of original issuance, if later.

The following table summarizes the calculation of unaudited pro forma basic and diluted net loss per common share:


(In thousands except share and per share data)	2017
Pro forma net loss per common share (unaudited)
Numerator
Net loss attributable to common stockholders	$	(26,554	)
Pro forma adjustments to eliminate changes in fair value of preferred stock warrant liability		46

Net loss used to compute pro forma net loss per share	$	(26,508	)
Denominator
Weighted average of common shares outstanding		2,028,224

Recent accounting pronouncements

In March 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share Based Payment Accounting (“ASU 2016-09”) as part of the FASB simplification initiative. The new standard provides for changes to accounting for stock compensation including 1) excess tax benefits and tax deficiencies related to share-based payment awards will be recognized as income tax expense in the reporting period in which they occur; 2) excess tax benefits will be classified as an operating activity in the statement of cash flow; 3) the option to elect to estimate forfeitures or account for them when they occur; and 4) increase tax withholding requirements threshold to qualify for equity classification. ASU 2016-09 is effective for public companies with annual periods and interim periods beginning after December 15, 2016. Early adoption is permitted. The Company intends to adopt this standard on January 1, 2018 and continues to analyze and assess the impact, if any, of this standard on its financial statements.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). The new standard requires the recognition of assets and liabilities arising from lease transactions on the balance sheet and the disclosure of key information about leasing arrangements. Accordingly, a lessee will recognize a lease asset for its right to use the underlying asset and a lease liability for the corresponding lease obligation. Both the asset and liability will initially be measured at the present value of the future minimum lease payments over the lease term. Subsequent measurement, including the presentation of expenses and cash flows, will depend on the classification of the lease as either a finance or an operating lease. Initial costs directly attributable to negotiating and arranging the lease will be included in the asset. For leases with a term of twelve months or less, a lessee can make an accounting policy election by class of underlying asset to not recognize an asset and corresponding liability. Lessees will also be required to provide additional qualitative and quantitative disclosures regarding the amount, timing and uncertainty of cash flows arising from leases. These disclosures are intended to supplement the amounts recorded in the financial statements and provide additional information about the nature of an organization’s leasing activities. The new standard will be effective for public companies with annual periods and interim periods beginning after December 15, 2018. Early adoption is permitted. In transition, lessees are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The transition guidance also provides specific guidance for sale and leaseback transactions, build-to-suit leases and amounts previously recognized in accordance with the business combinations guidance for leases. The Company intends to adopt this standard on January 1, 2020 and continues to analyze and assess the impact, if any, of this standard on its financial statements.

In May 2014, the FASB issued ASU 2014-09 (ASC606), Revenue from Contracts with Customers. This ASU, as amended by ASU 2015-14, affects any entity that either enters into contracts with customers to transfer goods and services or enters into contracts for the transfer of nonfinancial assets. ASU 2014-09 will replace most existing revenue recognition guidance in GAAP when it becomes effective. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under the currently effective guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 is effective for public companies with annual periods beginning after December 15, 2018 and for interim periods beginning after December 15, 2019. Early adoption is permitted. The Company intends to adopt this standard on January 1, 2019 and continues to analyze and assess the impact, if any, of this standard on its financial statements.

In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting. ASU 2017-09 clarifies when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award changes as a result of the change in terms or conditions. ASU 2017-09 will be applied prospectively to awards modified on or after the adoption date. ASU 2017-09 is effective for public companies for annual and interim periods beginning after December 15, 2017. Early adoption is permitted. The Company intends to adopt this standard on January 1, 2019, and continues to analyze and assess the impact, if any, of this standard on its financial statements.

Property and Equipment

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Property and Equipment

Note 3. Property and Equipment

Property and equipment consisted of the following:


	DECEMBER 31,
(In thousands)	2016			2017
Lab equipment	$	375		$	860
Furniture and fixtures		103			128
Computer equipment		50			100
Office equipment		26			78
Software		16			52
Leasehold improvements		10			10

		580			1,228
Less accumulated depreciation and amortization		(268	)		(440	)

Property and equipment, net	$	312		$	788

Depreciation and amortization expense relating to property and equipment was $116,000 and $177,000 for the years ended December 31, 2016 and 2017, respectively.

Accrued Expenses

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Payables and Accruals [Abstract]

Accrued Expenses

Note 4. Accrued Expenses

Accrued expenses consist of the following:


(In thousands)	DECEMBER 31, 2017		SEPTEMBER 30, 2018
Accrued employee costs	$	566	$	2,759
Accrued research costs		1,581		2,739
Other		410		762

Accrued expenses	$	2,557	$	6,260

Note 4. Accrued Expenses

Accrued expenses consist of the following:


	DECEMBER 31,
(In thousands)	2016		2017
Accrued employee costs	$	744	$	1,581
Accrued research costs		70		566
Other		88		410

Accrued expenses	$	902	$	2,557

Convertible Preferred Stock	9 Months Ended	12 Months Ended
Convertible Preferred Stock	Sep. 30, 2018	Dec. 31, 2017
Equity [Abstract]
Convertible Preferred Stock	Note 6. Convertible Preferred Stock In February 2018, the Company issued an additional 707,680 shares of Series C convertible preferred stock for net proceeds of $4.4 million. During the second quarter of 2018, a majority of the holders of the Company’s convertible preferred stock elected to have their shares converted into common stock, therefore, all outstanding shares of preferred stock were converted into 11,837,073 shares of common stock at a conversion rate of 1:1.78112 upon the closing of the Company’s IPO on June 25, 2018. Prior to the conversion of the convertible preferred stock into common stock; the holders of the Company’s convertible preferred stock were entitled to receive non-cumulative dividends at the rate of 8% of the purchase price per annum in preference to any dividends to the holders of the common stock, payable as and if when declared by the Board of Directors. No such dividends were declared by the Company’s Board of Directors. The holders of the convertible preferred stock also were entitled to participate pro rata in any dividends paid to the holders of the common stock on an as-converted basis. No dividends were declared by the Company’s Board of Directors.	Note 5. Convertible Preferred Stock The holders of the Company’s Preferred Stock will be entitled to receive non-cumulative dividends at the rate of 8% of the purchase price per annum in preference to any dividends to the holders of the common stock, payable as and if when declared by the Board of Directors. The Board has not declared any dividends as of December 31, 2017. The holders of the Preferred Stock also will be entitled to participate pro rata in any dividends paid to the holders of the common stock on an as-converted basis. Upon the liquidation of the Company, the holders of Preferred Stock will be entitled to receive, in preference to the holders of the common stock, an amount equal to $1.02 per share for Series A Convertible Preferred Stock, $3.319 per share for Series B Convertible Preferred Stock and $6.2705 per share for Series C Convertible Preferred Stock plus any declared but unpaid dividends (the “Liquidation Preference”). After the payment of the Liquidation Preference in full, the remaining assets or other property of the Company will be distributed ratably to the holders of the common stock and the Preferred Stock on an as converted basis. A merger or consolidation involving the Company, a sale of voting control of the Company or the sale of all or substantially all of the assets of the Company will be deemed to be a liquidation for this purpose. The holders of the Preferred Stock will have the right to convert their shares (including declared, but unpaid dividends thereon) into shares of the Company’s common stock at any time. The initial conversion rate will be 1:1.78112 subject to customary anti-dilution provisions. The Preferred Stock will convert automatically into common stock upon the election of the holders of a majority of the outstanding Preferred Stock holders; or the closing of a firmly underwritten public offering of shares of the Company’s common stock at a public offering price per share (prior to underwriter commissions and expenses) that is not less than $16.74 per share in an offering with aggregate proceeds to the Company of not less than $30,000,000. Prior to completion of the Company’s initial public offering, the holders of the Series C Convertible Preferred Stock are entitled to elect two board members and the holders of Series A and B Convertible Preferred Stock are entitled to elect two board members.

Warrants

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Warrants [Abstract]

Warrants

Note 7. Warrants

In 2014 the Company issued 19,931 warrants (“2014 Warrants”) to certain investors. The 2014 Warrants allow each holder to purchase one share of common stock for $5.912. There have been no exercises of 2014 Warrants and as such all 19,931 warrants were outstanding as of September 30, 2018.

As part of the Loan and Security Agreement discussed in Note 5, “Long-term Debt,” in the notes to unaudited condensed financial statements, the Lenders receive warrants equal to 3.0% of the principal borrowing amounts concurrent with the borrowing. The warrants represent a right for the lender to purchase shares of the Company’s common stock at an initial exercise price of $11.169 per share. The Company issued 53,720 warrants (“Term A Warrants”) upon the drawdown of the Term A Loan in February 2018 and the Company issued 40,292 warrants (“Term B Warrants”) upon the drawdown of the Term B Loan in September 2018. There have been no exercises of Term A Warrants or Term B Warrants and as such all 53,720 warrants and 40,292 warrants were outstanding as of September 30, 2018, respectively.

Because the warrants are a freestanding instrument, indexed to the Company’s stock, they do not meet the criteria for equity classification. Therefore warrants are liability classified and subject to remeasurement at each reporting period until they are exercised, expired, or otherwise settled. The initial fair value of the warrant liability was recorded with a corresponding offset to deferred debt cost which is a reduction to the notional value of the debt.

The Company recognized a gain (loss) of $(149,000), $(131,000) and $343,000 upon the change in fair value of the warrants during the nine months ended September 30, 2018 related to the 2014 Warrants, the Term A Warrants and the Term B Warrants, respectively. The Company recognized a loss of $(32,000) upon the change in fair value of the 2014 Warrants during the nine months ended September 30, 2017.

As of September 30, 2018, the following warrants were outstanding:


	OUTSTANDING SHARES		EXERCISE PRICE PER SHARE		EXPIRATION DATE
2014 Warrants		19,931	$	5.912		August 2020
Term A Warrants		53,720	$	11.169		February 2025
Term B Warrants		40,292	$	11.169		September 2025

		113,943

Note 6. Warrants

In 2013 the Company issued 69,000 Series A Convertible Preferred Stock warrants (“Series A Warrants”). The holder of each Series A Warrant was entitled to purchase one share of Series A Convertible Preferred Stock for $1.02. In 2016 47,791 warrants were exercised and the remaining Series A Warrants expired. There were no Series A Warrants outstanding as of December 31, 2016 and 2017.

In 2014 the Company issued 35,504 warrants (“Series B Warrants”) to certain investors. The Series B Warrants allow each holder to purchase one share of Series B Preferred stock for $3.319 and they expire in August of 2020. There have been no exercises of Series B Warrants as of December 31, 2017 and as such all 35,504 warrants were outstanding as of December 31, 2016 and 2017.

Commitments and Contingencies

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 8. Commitments and Contingencies

Commitments

The Company has non-cancellable operating leases for office space, which expire at various times through 2024. The non-cancellable office lease agreements provide for monthly lease payments, which increase during the term of each lease agreement. In the first quarter of 2018, the Company signed a new lease for office space in Chicago, Illinois with remaining future minimum lease payments of approximately $49,000 in 2018, $84,000 in 2019, $210,000 in 2020, $219,000 in 2021, $228,000 in 2022, and $524,000 in 2023 and thereafter.

Total rent expense under these operating leases was approximately $841,000 and $304,000 for the nine months ended September 30, 2018 and 2017, respectively.

Note 7. Commitments and Contingencies

Commitments

The Company has non-cancellable operating leases for office space and equipment, which expire at various times through 2024. The non-cancellable office lease agreements provide for monthly lease payments, which increase during the term of the lease. Future minimum lease payments under operating leases at December 31, 2017 are as follows:


(In thousands)
2018	$	730
2019		859
2020		834
2021		1,123
2022		1,148
Thereafter		701

Total minimum lease payments	$	5,395

Total rent expense under these operating leases was approximately $268,000 and $526,000 for the years ended December 31, 2016 and 2017, respectively.

The Company has an outstanding letter of credit for $58,000 used to secure a lease in San Diego, California.

Through December 31, 2017, the Company has received $760,000 out of an expected $872,000 in grant proceeds for the development of a stable liquid glucagon for use in an artificial pancreas. Under the terms of the agreement, the Company will be required to pay up to four times the award received upon the commercialization of glucagon for use in the artificial pancreas. If the Company undergoes a change in control, then the Company will be required to pay a mid-single digit percentage of the gross proceeds, capped at four times the award amount less any amounts already paid. Additionally, if sales of glucagon for use in the artificial pancreas exceed $750 million in the first five years after the first commercial sale, then the Company would be required to make an additional payment equal to the original award amount.

The Company has received a grant for $929,000 to help fund its exercise induced hypoglycemia (“EIH”) program. Under terms of this agreement and upon the commercialization of an EIH product, the Company will be required to make royalty payments based on a low double-digit percentage of annual gross sales of an EIH product, capped at $500,000 annually. If the Company undergoes a change in control, the Company will pay a mid-single digit percentage of the consideration capped at two times the award amount less any amounts already paid. Additionally, if sales exceed $1 billion, the Company will be required to make a milestone payment equal to two times the award amount.

The Company has received a grant for $1,004,000 to help fund its Type 1 Diabetes chronic glucagon programs. Under terms of this agreement the Company will be required to pay up to two times the award amount upon the commercialization of any chronic glucagon program. These amounts are a low double-digit percentage of annual gross sales of all Type 1 Diabetes chronic glucagon programs, capped at $500,000 annually. If the Company undergoes a change in control, then it will pay a mid-single digit percentage of the consideration capped at two times the award amount less any amounts already paid. Additionally, for each chronic glucagon program where sales exceed $500 million, the Company will be required to pay an additional amount equal to two times the award amount.

Litigation

From time to time, the Company may become involved in various legal actions arising in the ordinary course of business. As of December 31, 2016 and 2017, management was not aware of any existing, pending or threatened legal actions that would have a material impact on the financial position or results of operations of the Company.

Shareholder Notes Receivables	12 Months Ended
Shareholder Notes Receivables	Dec. 31, 2017
Receivables [Abstract]
Shareholder Notes Receivables	Note 8. Shareholder Notes Receivables In November 2014, the Company accepted Notes Receivables totaling $107,000 from its then Chief Executive Officer (CEO) and a member of the Company’s Board of Directors, to exercise certain stock options. The Notes Receivables carried an interest rate of 1.93%, were payable in equal installments over 60 months and were collateralized by the underlying common stock purchased as a part of the stock option exercise and thus were recorded as a deduction to stockholder’s equity. The Board member paid his Note Receivable in full upon his resignation from the Board in 2016. The Company agreed to forgive the unpaid portion of the CEO’s Note Receivable as part of his severance package in connection with this separation from the Company in January 2017. As a result, the CEO’s Note Receivable of $73,000 was fully reserved at December 31, 2016 and written off in January 2017.

- Definition

The entire disclosure for claims held for amounts due a entity, excluding financing receivables. Examples include, but are not limited to, trade accounts receivables, notes receivables, loans receivables. Includes disclosure for allowance for credit losses.

+ References + Details

Stock Compensation Plan

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Compensation Plan

Note 9. Stock Compensation Plan

In 2011 the Company adopted the 2011 Stock Option Issuance Plan (“2011 Plan”) and subsequently amended it to authorize the Board of Directors to issue up to 4,714,982 incentive grant and non-statutory awards.

The 2018 Stock Option and Incentive Plan (“2018 Plan”) was adopted by our Board of Directors in April 2018 and approved by our stockholders in June 2018 to award up to 1,822,000 shares of our common stock. This plan became effective on the date immediately prior to the effectiveness of the Company’s IPO registration statement. The 2018 Plan replaced the 2011 Plan as our Board of Directors determined not to make additional awards under the 2011 Plan following the closing of our IPO, which occurred in June 2018. The 2018 Plan allows the compensation committee to make equity-based and cash-based incentive awards to our officers, employees, directors and other key persons (including consultants). As of September 30, 2018, there were 1,539,190 awards available for future issuance.

Stock options are granted with an exercise price equal to the market price of the Company’s stock at the date of grant. Stock option awards typically vest over either two years or four years after the grant date and expire ten years from the grant date.

The fair value of each option is estimated on the date of grant using a Black-Scholes option valuation model that uses the assumptions noted in the following table. The expected life of options represents the period of time that options granted are expected to be outstanding. The risk-free interest rate for periods during the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant. For fiscal 2018, the expected volatility is based on the historical volatility of certain peer companies over the most recent period corresponding to the expected life as of the grant date. The expected dividend yield is based on the expected annual dividend as a percentage of the market value of the Company’s ordinary shares as of the grant date. The Company uses historical data to estimate option exercises and employee terminations within the valuation model.

The fair value of stock options granted was estimated with the following weighted average assumptions:


	NINE MONTHS ENDED SEPTEMBER 30,
	2017			2018
Expected term		6.1			6.0
Risk-free interest rate		2.05	%		2.80	%
Expected volatility		61.23	%		58.55	%
Expected dividends		—			—

Stock option activity for employee awards for the nine months ended September 30, 2018 was as follows:


	UNITS			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE CONTRACTUAL LIFE (YEARS)
Outstanding—January 1, 2018		1,946,230		$	1.66		8.70
Issued		1,167,077			12.13
Exercised		(181,884	)		1.42
Forfeited		(185,003	)		1.94

Outstanding—September 30, 2018		2,746,420		$	6.26		8.74

Exercisable—September 30, 2018		2,347,080		$	4.54		8.60

Vested and expected to vest at September 30, 2018		2,470,131		$	6.07		8.70

The weighted average fair value of awards granted during the nine months ended September 30, 2018 was $6.53 per share. The total intrinsic value of options exercised during the nine months ended September 30, 2018 was $1.7 million. The aggregate intrinsic value of awards vested and expected to vest as of September 30, 2018 was $29.3 million.

The Company also granted stock options to non-employees. These awards are marked to fair value at the end of each reporting period until they vest. Stock option activity for these awards for the nine months ended September 30, 2018 was as follows:


	UNITS			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE CONTRACTUAL LIFE (YEARS)
Outstanding—January 1, 2018		33,125		$	1.91		6.75
Issued		—			—
Exercised		(26,337	)		2.17
Forfeited		—			—

Outstanding—September 30, 2018		6,788		$	1.09		4.89

Exercisable—September 30, 2018		6,737		$	1.09		4.89

Vested and expected to vest at September 30, 2018		6,737		$	1.09		4.89

The aggregate intrinsic value of awards vested and expected to vest at September 30, 2018 was $111,000. The aggregate intrinsic value of awards exercisable as of September 30, 2018 was $111,000. The company recognized expense associated with these awards of $114,000 and $12,000 for the nine months ended September 30, 2018 and 2017, respectively.

The following table summarizes the reporting of total stock-based compensation expense resulting from employee and non-employee stock options:


	NINE MONTHS ENDED SEPTEMBER 30,
(in thousands)	2017		2018
Research and development	$	46	$	398
General and administrative		305		751

Total stock-based compensation	$	351	$	1,149

At September 30, 2018, there was a total of $6.9 million of unrecognized compensation expense that is expected to be recognized over a weighted average period of 1.51 years.

Note 9. Stock Compensation Plan

In 2011 the Company adopted the 2011 Stock/Option Issuance Plan (“2011 Plan”) and subsequently amended to authorize the Board of Directors to issue up to 4,378,116 incentive grant and non-statutory awards. Options and restricted stock granted to employees under the 2011 Plan typically vest over a 48-month period and options and restricted stock granted to non-employee directors vest over a 24-month period. All stock awards typically expire 10 years after they were issued. Subsequent to December 31, 2017 the shareholders approved an increase of 336,866 incentive grant and non-statutory awards allowed to be granted under the 2011 Plan.

The fair value of stock options was estimated with the following weighted average assumptions:


	YEARS ENDED DECEMBER 31,
	2016			2017
Expected term		5.88			6.06
Expected volatility		61.46	%		61.10	%
Risk-free interest rate		1.48	%		2.06	%
Expected dividends		—			—

Stock option activity for employee awards for the year ended December 31, 2016 and 2017 is as follows:


	UNITS			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE CONTRACTUAL LIFE (YEARS)
Outstanding—January 1, 2016		364,612		$	1.32		6.33
Issued		138,115			2.71
Exercised		(12,538	)		0.87
Forfeited		(9,350	)		1.23

Outstanding—December 31, 2016		480,838			1.69		6.71
Issued		1,642,565			1.64
Exercised		(117,318	)		1.59
Forfeited		(13,256	)		1.83
Expired		(46,599	)		1.53

Outstanding—December 31, 2017		1,946,230		$	1.66		8.71

Exercisable—December 31, 2017		1,709,929		$	1.64		8.70

Vested and expected to vest at December 31, 2017		1,735,470		$	1.66		8.70

The weighted average grant date fair value of awards granted during the years ended December 31, 2016 and 2017 was $1.55 and $0.94 per share, respectively. The total intrinsic value of options exercised during the years ended December 31, 2016 and 2017 was $9,000 and $1,258,000 respectively. The aggregate intrinsic value of awards vested and expected to vest as of December 31, 2016 and 2017 was $122,000 and $7,422,000, respectively.

Restricted stock awards for employees for the 2011 Plan for the years ended December 31, 2016 and 2017 is as follows:


	SHARES
Outstanding—January 1, 2016		96,849
Granted		103,867
Vested		(99,898	)

Outstanding—December 31, 2016		101,118
Vested		(101,118	)

Outstanding—December 31, 2017		—

The weighted average grant date fair value of awards issued in 2016 was $294,000 and the intrinsic fair value of shares vested and expected to vest during the year ended December 31, 2016 was $157,000. There were no awards granted during 2017 or outstanding as of December 31, 2017.

The following table summarizes the reporting of total stock-based compensation expense resulting from employee and non-employee stock options and restricted stock awards:


	YEARS ENDED DECEMBER 31,
(In thousands)	2016		2017
Research and development	$	78	$	62
General and administrative		462		437

Total stock-based compensation	$	540	$	499

There was a total of $1,311,000 of unrecognized compensation expense that is expected to be recognized over a weighted average period of 1.34 years.

The Company also granted stock options to non-employees. These awards are marked to fair-value at the end of each reporting period. Stock option activity for these awards for the years ended December 31, 2016 and 2017 is as follows:


	UNITS			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE CONTRACTUAL LIFE (YEARS)
Outstanding—January 1, 2016		27,510			0.89		7.15
Issued		14,036			2.83
Exercised		(12,866	)		0.82
Forfeited		(1,170	)		0.82

Outstanding—December 31, 2016		27,510			1.91		7.75
Issued		5,614			1.55

Outstanding—December 31, 2017		33,124		$	1.91		6.75

Exercisable—December 31, 2017		27,510		$	1.91		6.75

Vested and expected to vest at December 31, 2017		27,510		$	1.91		6.74

The aggregate intrinsic value of awards vested and expected to vest at December 31, 2016 and 2017 was $8,000 and $110,000 respectively. The aggregate intrinsic value of awards exercisable as of December 31, 2016 and 2017 was $8,000 and $111,000, respectively. The company recognized expense associated with these awards of $8,000 and $35,000 for the years ended December 31, 2016 and 2017, respectively.

Defined Contribution Plan	12 Months Ended
Defined Contribution Plan	Dec. 31, 2017
Postemployment Benefits [Abstract]
Defined Contribution Plan	Note 10. Defined Contribution Plan The Company sponsors an employee retirement plan qualifying under Section 401(k) of the Internal Revenue Code for all eligible employees in the United States. Employees become eligible to contribute to the plan upon meeting certain age requirements and 30 days of service. Currently the company does not make any contributions to the plan.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

Note 11. Income Taxes

Due to reported losses, the Company recorded no income tax expense for the years ended December 31, 2016 and 2017. A reconciliation of the expected income tax benefit computed using the federal statutory income tax rate of 34% to the Company’s effective income tax rate is as follows:


	DECEMBER 31,
(In thousands)	2016			2017
Income tax using the federal statutory tax rate	$	(4,491	)	$	(9,028	)
Impact of rate change		—			7,478
Research and development and orphan drug credit		(655	)		(517	)
Permanent adjustments to expenses		(3	)		76
Stock compensation		145			42
Prior year adjustment		—			(100	)
Changes in valuation allowance		5,004			2,049

Total income taxes	$	—		$	—

During the years ended December 31, 2016 and 2017, the Company had no interest and penalties related to income taxes.

Deferred income taxes reflect the net tax effects of temporary difference between the carrying amount of the assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The Company has established a valuation allowance due to the uncertainties regarding the realization of the deferred tax assets based on the Company’s lack of earning’s history. Significant components of the Company’s deferred tax assets and liabilities are as follows:


	DECEMBER 31,
(In thousands)	2016			2017
Deferred tax assets
Net operating losses	$	10,547		$	11,715
Research credits		1,462			2,045
Stock compensation		5			49
Other temporary differences		202			349
Valuation allowance		(12,157	)		(14,124	)

Total assets		59			34
Deferred tax liabilities
Fixed and intangible assets		(59	)		(34	)

Total liabilities		(59	)		(34	)

Net deferred tax assets	$	—		$	—

As of December 31, 2016 and 2017, the Company had federal net operating loss carryforwards (“NOL”) of $31,011,000 and $55,786,000, respectively. As of December 31, 2016 and 2017, the Company had federal research and orphan drug credit carryforwards of $1,462,000 and $2,045,000, respectively. If not utilized, these NOLs and research and orphan drug credit carryforwards will expire between 2025 and 2036.

Impacts of the Tax Cuts and Jobs Act

On December 22, 2017, the Tax Cuts and Jobs Act (H.R. 1) (the “Tax Act”) was signed into law. The Tax Act contains significant changes to corporate taxation, including (i) the reduction of the corporate income tax rate to 21%, (ii) the acceleration of expensing for certain business assets, (iii) the one-time transition tax related to the transition of U.S. international tax from a worldwide tax system to a territorial tax system, (iv) the repeal of the domestic production deduction, (v) additional limitations on the deductibility of interest expense, and (vi) expanded limitations on executive compensation. The key impacts of the Tax Act on the Company’s financial statements for the year ended December 31, 2017, were the re-measurement of deferred tax balances to the new corporate tax rate. While the Company has not yet completed the assessment of the effects of the Tax Act, the Company was able to determine reasonable estimates for the impacts of the key items specified above, thus it reported provisional amounts for these items. In accordance with Staff Accounting Bulletin No. 118 (“SAB 118”), the Company is providing additional disclosures related to these provisional amounts. In order to calculate the effects of the new corporate tax rate on its deferred tax balances, ASC 740 “Income Taxes” (“ASC 740”) required the re-measurement of the Company’s deferred tax balances as of the enactment date of the Tax Act, based on the rates at which the balances were expected to reverse in the future. The provisional amount determined, and recorded, for the re-measurement of its deferred tax balances resulted in a net reduction in deferred tax assets of $7,478,000 and a corresponding reduction in the valuation allowance of $7,478,000.

The aforementioned provisional amounts related to the deferred tax balances are based on information available at this time and may change due to a variety of factors, including, among others, (i) anticipated guidance from the U.S. Department of Treasury about implementing the Tax Act, (ii) potential additional guidance from the Securities and Exchange Commission or the FASB related to the Tax Act and (iii) management’s further assessment of the Tax Act and related regulatory guidance. The Company is not complete in its assessment of the impact of the Tax Act on its business and financial statements. While the effective date of most of the provisions of the Tax Act do not apply until the Company’s tax year beginning January 1, 2018 it will continue the assessment of the impact of the Tax Act on its business and financial statements throughout the one-year measurement period as provided by SAB 118.

Fair Value Measurement

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurement

Note 10. Fair Value Measurements

Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements are classified and disclosed in one of the following categories:

Level 1: Measured using unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.

Level 2: Measured using quoted prices in active markets for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or inputs, other than quoted prices in active markets, that are observable either directly or indirectly; and

Level 3: Measured based on prices or valuation models that required inputs that are both significant to the fair value measurement and less observable from objective sources (i.e., supported by little or no market activity).

Fair value measurements are classified based on the lowest level of input that is significant to the measurement. The Company’s assessment of the significance of a particular input to the fair value measurement requires judgment, which may affect the valuation of the assets and liabilities and their placement within the fair value hierarchy levels. The determination of the fair values stated below takes into account the market for its financial assets and liabilities, the associated credit risk and other factors as required. The Company considers active markets as those in which transactions for the assets or liabilities occur in sufficient frequency and volume to provide pricing information on an ongoing basis.

The following tables present the Company’s fair value hierarchy for those assets and liabilities measured at fair value as of December 31, 2017 and September 30, 2018:


(in thousands)	TOTAL AS OF DECEMBER 31, 2017		LEVEL 1		LEVEL 2		LEVEL 3
Current Assets
Money market funds ^(a)	$	39,124	$	39,124	$	—	$	—

Other current liabilities
Warrant liabilities	$	93	$	—	$	—	$	93


(in thousands)	TOTAL AS OF SEPTEMBER 30, 2018		LEVEL 1		LEVEL 2		LEVEL 3
Current Assets
Cash and cash equivalents:
Money market funds	$	72,746	$	72,746	$	—	$	—
Commercial paper		2,999		2,999		—		—

Total cash and cash equivalents	$	75,745	$	75,745	$	—	$	—

Short-term investments:
U.S. government securities	$	32,212	$	32,212	$	—	$	—
Corporate securities		12,156		—		12,156		—
Agency securities		10,928		—		10,928		—

Total short-term investments	$	55,296	$	32,212	$	23,084	$	—

Other current liabilities
Warrant liabilities	$	1,042	$	—	$	—	$	1,042

^(a)

The money market funds noted above are included in cash and cash equivalents.

There were no investments in commercial paper or short-term investments as of December 31, 2017.

The fair value of the Company’s warrant liabilities at inception and for subsequent mark-to-market fair value measurements is based on management’s valuation model and expected methods and timing of settlement. These estimates are prepared using models that consider various inputs including: (a) the Company’s estimated future cash flows, (b) time value, (c) current market conditions, and (d) other relevant economic measures.

The Company has determined that the warrant liabilities’ fair values are Level 3 items within the fair value hierarchy. The following table presents the changes in the warrant liabilities:


(in thousands)
Balance at December 31, 2017	$	93
Fair value of Term A Warrants issued under the Loan and Security Agreement		326
Fair value of Term B Warrants issued under the Loan and Security Agreement		686
Change in fair value of warrants		(63	)

Balance at September 30, 2018		1,042

There were no transfers between any of the levels of the fair value hierarchy during the nine months ended September 30, 2018.

Note 12. Fair Value Measurement

Level 1: Measured using unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.

Level 2: Measured using quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability.

The carrying amounts of cash and cash equivalents, grants receivable, and accounts payables approximate their fair values due to the short-term maturities of these instruments.

The fair value of the Company’s warrant liabilities at inception and for subsequent mark-to-market fair value measurements, are based on management’s valuation model and expected methods and timing of settlement. These estimates are prepared using models that consider various inputs including: (a) the Company’s estimated future cash flows, (b) time value, and (c) current market conditions, as well as other relevant economic measures. The Company has determined that the warrant liabilities fair values are Level 3 items within the fair value hierarchy. The following table presents the changes in the warrant liabilities:


(In thousands)
Balance at January 1, 2016	$	180
Fair value of Series A warrants expired/exercised		(109	)
Changes in fair value of warrants		(24	)

Balance at December 31, 2016		47
Changes in fair value of warrants		46

Balance at December 31, 2017	$	93

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Related Party Transaction	12 Months Ended
Related Party Transaction	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transaction	Note 13. Related Party Transaction During 2017 the Company paid a spouse of an officer $37,000 to help with the development of the Company’s website.

Subsequent Events

12 Months Ended

Dec. 31, 2017

Subsequent Events [Abstract]

Subsequent Events

Note 14. Subsequent Events

Management reviews events and transactions occurring after the balance sheet date for potential recognition and disclosure in the financial statements. Management has evaluated subsequent events through March 21, 2018, the date on which the financial statements were available to be issued.

In February 2018, the Company entered into a lease for office space in Chicago, Illinois that expires in November 2024, and entered into a letter of credit for $85,000 to secure the lease. Annual minimum lease payments for the next five years are included in the table below:


(In thousands)
2018	$	163
2019		202
2020		210
2021		219
2022		228
Thereafter		462

Total minimum lease payments	$	1,484

In February 2018, the Company sold 707,680 shares of Series C Convertible Preferred Stock for $6.2705 per share resulting in proceeds of $4.4 million with the same rights and preferences as the Series C Preferred Stock disclosed in Note 5.

In February 2018, the Company entered into the Loan Agreement, providing a senior secured loan facility of up to an aggregate principal amount of $45.0 million, comprising a $20.0 million drawdown in February 2018, and an additional $25.0 million which can be borrowed in two additional tranches. The second tranche is $15.0 million and is available beginning upon our submission of our NDA for our Gvoke HypoPen until the earlier of September 30, 2018 or the 30th day following such NDA submission. The third tranche is $10.0 million and is available beginning upon approval of our Gvoke HypoPen NDA by the FDA until the earlier of September 30, 2019 or the 30th day following NDA approval by the FDA.

The interest rate under the Loan Agreement is the thirty-day U.S. LIBOR rate plus 6.75%. Payments on the Loan Agreement are interest only for the first 24 months, which can be extended by an additional twelve months if the third tranche is drawn. The total term of the loan is 59 months and the principal payments will begin in either 36 or 24 months, contingent on the third tranche being drawn.

Pursuant to the Loan Agreement, the Company provided a first priority security interest in all existing and after-acquired assets, excluding intellectual property and certain other assets, owned by us. There is a negative pledge on intellectual property owned by the Company.

The Company also issued warrants to the Lenders to purchase the Company’s Series C Preferred stock at an exercise price of $6.2705. The number of warrants issued to Lenders is equal to the total principal of each funded tranche multiplied by 3.0%, which is then divided by $6.2705. As of March 1, 2018, a total of 95,686 warrants have been issued in connection with the Loan Agreement.

The Loan Agreement allows the Company to voluntarily prepay the outstanding amounts thereunder, but not less than $2.0 million of the outstanding principal at any time. A prepayment fee of 1.5% would be assessed on the prepaid principal through the interest-only period. A final payment fee of 6.5% multiplied by the original principal amount of each tranche drawn is due upon the earlier to occur of the maturity date of the Loan Agreement, the acceleration of the Loan Agreement or prepayment of such borrowings. The Loan Agreement includes a non-utilization fee of 2.0% multiplied by the principal amount of tranche three payable to lenders in October 2019, if the Company does not elect to draw the third Tranche.

Reverse Stock Split and Initial Public Offering	9 Months Ended	12 Months Ended
Reverse Stock Split and Initial Public Offering	Sep. 30, 2018	Dec. 31, 2017
Federal Home Loan Banks [Abstract]
Reverse Stock Split and Initial Public Offering	Note 3. Reverse Stock Split and Initial Public Offering On June 8, 2018, the Company effectuated a 1-for-1.78112 reverse stock split of its outstanding common stock, which was approved by the Company’s board of directors on May 22, 2018 and by the Company’s stockholders on June 8, 2018. The reverse stock split resulted in an adjustment to the preferred stock conversion prices to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented. The shares of common stock retained a par value of $0.0001 per share. Accordingly, the stockholders’ deficit reflects the reverse stock split by reclassifying from common stock to additional paid in capital an amount equal to the par value of the decreased shares resulting from the reverse stock split. On June 25, 2018, the Company closed the IPO of its common stock pursuant to a registration statement on Form S-1, as amended. The Company sold an aggregate of 6,555,000 shares of common stock under the registration statement at a public offering price of $15.00 per share, including 855,000 shares of common stock pursuant to the exercise of the underwriters’ option to purchase additional shares. Net proceeds from the offering were approximately $89.0 million, after deducting underwriting discounts and commissions, as well as other offering expenses. Upon closing the IPO, all outstanding shares of the Company’s Series A, B and C convertible preferred stock were converted into 11,837,073 shares of common stock.	Note 15. Reverse Stock Split On June 8, 2018, the Company effectuated a 1-for-1.78112 reverse stock split of its outstanding common stock, which was approved by the Company’s board of directors on May 22, 2018 and by the Company’s stockholders on June 8, 2018. The reverse stock split resulted in an adjustment to the preferred stock conversion prices to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented. The shares of common stock retained a par value of $0.0001 per share. Accordingly, the stockholders’ deficit reflects the reverse stock split by reclassifying from common stock to additional paid in capital an amount equal to the par value of the decreased shares resulting from the reverse stock split.

Long-term Debt

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Long-term Debt

Note 5. Long-term Debt

Senior Secured Loan Facility

In February 2018, the Company entered into the Loan and Security Agreement that provides a senior secured loan facility of up to an aggregate principal amount of $45.0 million. The first tranche was $20.0 million and was drawn down in February 2018 (“Term A Loan”). The second tranche was $15.0 million and was drawn down in September 2018 (“Term B Loan”). The third tranche is $10.0 million and is available beginning upon approval of the Company’s Gvoke HypoPen New Drug Application (“NDA”) by the U.S. Food & Drug Administration (”FDA”) until the earlier of September 30, 2019 or the 30^th day following NDA approval by the FDA.

The interest rate under the Loan and Security Agreement is the thirty-day U.S. LIBOR rate plus 6.75%, which was approximately 8.86% as of September 30, 2018. Payments on the Loan and Security Agreement are interest only for the first 24 months, which can be extended by an additional twelve months if the third tranche is drawn. The total term of the loan is fifty-nine months, and the principal payments will begin in either 36 months or 24 months, contingent on the third tranche being drawn.

Pursuant to the Loan and Security Agreement, the Company provided a first priority security interest in all existing and future-acquired assets, excluding intellectual property and certain other assets, owned by the Company. The Loan and Security Agreement contains a negative pledge on intellectual property owned by the Company. The Company also issued warrants to the Lenders to purchase common stock, which is further discussed in Note 7, “Warrants,” of the notes to unaudited condensed financial statements.

The Loan and Security Agreement allows the Company to voluntarily prepay the outstanding amounts thereunder, but not less than $2.0 million of the outstanding principal at any time. Prior to April 1, 2020, the Company is subject to a prepayment penalty equal to 1.50% of the principal amount being prepaid. In the event the Company draws on the third tranche, the period subject to 1.50% prepayment is extended to April 1, 2021. No prepayment fee exists for prepayments made after April 1, 2020, or April 1, 2021 in the event the third tranche is issued. A final payment fee of 6.5% multiplied by the original principal amount of each tranche drawn is due upon the earlier to occur of the maturity date of the Loan and Security Agreement, the acceleration of the Loan and Security Agreement or prepayment of such borrowings. The Loan and Security Agreement includes a non-utilization fee of 2.0% multiplied by the principal amount of tranche three payable to Lenders in October 2019, if the Company elects not to draw the third tranche.

The Loan and Security Agreement also contains customary indemnification obligations and customary events of default, including, among other things, failure to fulfill certain obligations under the Loan and Security Agreement and the occurrence of a material adverse change in the Company’s business, operations or condition, a material impairment of the prospect of repayment of any portion of the loan, or a material impairment in the perfection or priority of the Lenders’ lien in the collateral or in the value of such collateral. In the event of default under the Loan and Security Agreement, the Company would be required to pay interest on principal and all other due and unpaid obligations at the current rate in effect plus 5%. All such interest would be payable on demand and in cash. Further, the Lenders would be entitled to exercise their remedies thereunder, including the right to accelerate the debt, upon which the Company may be required to repay all amounts then outstanding under the Loan and Security Agreement.

The Loan and Security Agreement includes certain restrictions on, among other things, the Company’s ability to incur additional indebtedness, change the name or location of the business, merge with or acquire other entities, pay dividends or make other distributions to holders of the Company’s capital stock, make certain investments, engage in transactions with affiliates, create liens, open new deposit accounts, sell assets or pay subordinated debt.

The components of debt are as follows:


(in thousands)	DECEMBER 31, 2017		SEPTEMBER 30, 2018
Term A Loan	$	—	$	20,000
Term B Loan		—		15,000
Less unamortized deferred cost		—		(3,358	)

Long-term debt	$	—	$	31,642

The following table sets forth the Company’s future minimum principal payments (in thousands):


2018	$	—
2019		—
2020		9,000
2021		12,000
2022		12,000
2023		2,000

	$	35,000

The Company incurred total debt issuance costs of $3.7 million, which are reflected as a direct reduction to the term loan balance and are being amortized into interest expense over the life of the loan using the effective interest method. For the nine months ended September 30, 2018, the Company recognized interest expense of $1,490,000, of which $312,000, was related to the amortization of debt issuance costs.

Short-Term Investments

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Short-Term Investments

Note 11. Short-Term Investments

The Company classifies its short-term investments as available-for-sale. Short-term investments comprise highly liquid investments with minimum “A” rated securities and as of September 30, 2018 consist of U.S. Treasury and agency bonds and corporate entity commercial paper and securities with maturities of more than three months but less than one year at the date of purchase. Short-term investments as of September 30, 2018 have an average maturity of 0.58 years. The investments are reported at fair value with unrealized gains or losses recorded in accumulated other comprehensive loss in the condensed balance sheets. Any differences between the cost and fair value of investments are represented by unrealized gains or losses. Refer to Note 10, “Fair Value Measurements,” of the notes to unaudited condensed financial statements for information related to the fair value measurements and valuation methods utilized.

The following table represents the Company’s available for sale short-term investments by major security type as of September 30, 2018:


(in thousands)	AMORTIZED COST		GROSS UNREALIZED LOSSES			TOTAL FAIR VALUE
Short-term investments:
Agency securities	$	10,938	$	(10	)	$	10,928
Corporate securities		12,166		(10	)		12,156
U.S. government securities		32,250		(38	)		32,212

Total short-term investments	$	55,354	$	(58	)	$	55,296

There were no investments in short-term securities as of December 31, 2017.

We review our available-for-sale investments for other-than-temporary impairment loss quarterly. We consider factors such as the duration, severity and the reason for the decline in value, the potential recovery period and our intent to sell. For debt securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis and (ii) the amortized cost basis cannot be recovered as a result of credit losses. During the quarter ended September 30, 2018, we did not recognize any other-than-temporary impairment losses. All marketable securities with unrealized losses have been in a loss position for less than twelve months.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Accounting Policies [Abstract]

Use of estimates

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and contingent liabilities and expenses included in the financial statements and accompanying notes. Actual results could differ from those estimates.

Grant Income

Grant Income

Revenue

Revenue

Research and development costs

Research and development costs

Stock-based compensation

Stock-based compensation

Income Taxes

Income Taxes

Cash and cash equivalents

Cash and cash equivalents

Cash and cash equivalents include demand deposits with financial institutions and liquid investments with original maturities of three months or less.

Concentrations of risk

Concentrations of risk

The Company has no off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.

Prepaid expenses and other current assets

Prepaid expenses and other current assets

Property and equipment

Property and equipment

Property and equipment are carried at cost less accumulated depreciation. Depreciation is calculated utilizing the straight-line method over the estimated useful lives of the respective assets:


Lab equipment			5 years
Computer equipment			5 years
Leasehold improvements			Lesser of useful life or lease term
Software			3-5 years
Furniture and fixtures			5 years
Office equipment			5 years

Impairment of long-lived assets

Impairment of long-lived assets

Deferred rent

Deferred rent

Preferred stock

Preferred stock

Warrants

Warrants

Fair value of financial instruments

Fair value of financial instruments

Segments

Segments

Net loss per common share

Net loss per common share


	SEPTEMBER 30,
	2017		2018
Convertible preferred stock		10,954,012		—
Warrants		19,931		113,943
Vested and unvested stock options		1,902,997		2,753,208

		12,876,940		2,867,151

Net loss per share

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2016 and 2017, as they would be antidilutive:


	YEARS ENDED DECEMBER 31,
	2016		2017
Convertible preferred stock		8,263,377		11,439,752
Warrants		19,931		19,931
Vested and unvested stock options		508,328		1,979,306

		8,791,636		13,438,989

Amounts in the table above reflect the common stock equivalents of the noted instruments.

The following table summarizes the calculation of unaudited pro forma basic and diluted net loss per common share:


(In thousands except share and per share data)	2017
Pro forma net loss per common share (unaudited)
Numerator
Net loss attributable to common stockholders	$	(26,554	)
Pro forma adjustments to eliminate changes in fair value of preferred stock warrant liability		46

Net loss used to compute pro forma net loss per share	$	(26,508	)
Denominator
Weighted average of common shares outstanding		2,028,224

Recent accounting pronouncements

Recent accounting pronouncements

In March 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share Based Payment Accounting (“ASU 2016-09”) as part of the FASB simplification initiative. The new standard provides for changes to accounting for stock compensation including 1) excess tax benefits and tax deficiencies related to share-based payment awards will be recognized as income tax expense in the reporting period in which they occur; 2) excess tax benefits will be classified as an operating activity in the statement of cash flow; 3) the option to elect to estimate forfeitures or account for them when they occur; and 4) increase tax withholding requirements threshold to qualify for equity classification. ASU 2016-09 is effective for public companies with annual periods and interim periods beginning after December 15, 2016. Early adoption is permitted. The Company intends to adopt this standard on January 1, 2018 and continues to analyze and assess the impact, if any, of this standard on its financial statements.

Impacts of the Tax Cuts and Jobs Act

Impacts of the Tax Cuts and Jobs Act

Debt issuance costs

Debt issuance costs

Equity financing costs

Equity financing costs

Summary of Significant Accounting Policies (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of Property and Equipment Estimated Useful Lives

Property and equipment are carried at cost less accumulated depreciation. Depreciation is calculated utilizing the straight-line method over the estimated useful lives of the respective assets:


Lab equipment			5 years
Computer equipment			5 years
Leasehold improvements			Lesser of useful life or lease term
Software			3-5 years
Furniture and fixtures			5 years
Office equipment			5 years

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share


	SEPTEMBER 30,
	2017		2018
Convertible preferred stock		10,954,012		—
Warrants		19,931		113,943
Vested and unvested stock options		1,902,997		2,753,208

		12,876,940		2,867,151

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2016 and 2017, as they would be antidilutive:


	YEARS ENDED DECEMBER 31,
	2016		2017
Convertible preferred stock		8,263,377		11,439,752
Warrants		19,931		19,931
Vested and unvested stock options		508,328		1,979,306

		8,791,636		13,438,989

Summary of Calculation of Unaudited Pro Forma Basic and Diluted Net Loss Per Common Share

The following table summarizes the calculation of unaudited pro forma basic and diluted net loss per common share:


(In thousands except share and per share data)	2017
Pro forma net loss per common share (unaudited)
Numerator
Net loss attributable to common stockholders	$	(26,554	)
Pro forma adjustments to eliminate changes in fair value of preferred stock warrant liability		46

Net loss used to compute pro forma net loss per share	$	(26,508	)
Denominator
Weighted average of common shares outstanding		2,028,224

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consisted of the following:


	DECEMBER 31,
(In thousands)	2016			2017
Lab equipment	$	375		$	860
Furniture and fixtures		103			128
Computer equipment		50			100
Office equipment		26			78
Software		16			52
Leasehold improvements		10			10

		580			1,228
Less accumulated depreciation and amortization		(268	)		(440	)

Property and equipment, net	$	312		$	788

Accrued Expenses (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Payables and Accruals [Abstract]

Accrued Expenses

Accrued expenses consist of the following:


(In thousands)	DECEMBER 31, 2017		SEPTEMBER 30, 2018
Accrued employee costs	$	566	$	2,759
Accrued research costs		1,581		2,739
Other		410		762

Accrued expenses	$	2,557	$	6,260

Accrued expenses consist of the following:


	DECEMBER 31,
(In thousands)	2016		2017
Accrued employee costs	$	744	$	1,581
Accrued research costs		70		566
Other		88		410

Accrued expenses	$	902	$	2,557

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Future Minimum Lease Payments under Operating Leases

Future minimum lease payments under operating leases at December 31, 2017 are as follows:


(In thousands)
2018	$	730
2019		859
2020		834
2021		1,123
2022		1,148
Thereafter		701

Total minimum lease payments	$	5,395

Subsequent Event [Member]

Schedule of Future Minimum Lease Payments under Operating Leases

Annual minimum lease payments for the next five years are included in the table below:


(In thousands)
2018	$	163
2019		202
2020		210
2021		219
2022		228
Thereafter		462

Total minimum lease payments	$	1,484

Stock Compensation Plan (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Stock-based Compensation Assumptions Used in Black-Scholes Option Valuation Model

The fair value of stock options granted was estimated with the following weighted average assumptions:


	NINE MONTHS ENDED SEPTEMBER 30,
	2017			2018
Expected term		6.1			6.0
Risk-free interest rate		2.05	%		2.80	%
Expected volatility		61.23	%		58.55	%
Expected dividends		—			—

The fair value of stock options was estimated with the following weighted average assumptions:


	YEARS ENDED DECEMBER 31,
	2016			2017
Expected term		5.88			6.06
Expected volatility		61.46	%		61.10	%
Risk-free interest rate		1.48	%		2.06	%
Expected dividends		—			—

Share-based Compensation, Activity

Stock option activity for employee awards for the year ended December 31, 2016 and 2017 is as follows:


	UNITS			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE CONTRACTUAL LIFE (YEARS)
Outstanding—January 1, 2016		364,612		$	1.32		6.33
Issued		138,115			2.71
Exercised		(12,538	)		0.87
Forfeited		(9,350	)		1.23

Outstanding—December 31, 2016		480,838			1.69		6.71
Issued		1,642,565			1.64
Exercised		(117,318	)		1.59
Forfeited		(13,256	)		1.83
Expired		(46,599	)		1.53

Outstanding—December 31, 2017		1,946,230		$	1.66		8.71

Exercisable—December 31, 2017		1,709,929		$	1.64		8.70

Vested and expected to vest at December 31, 2017		1,735,470		$	1.66		8.70


	UNITS			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE CONTRACTUAL LIFE (YEARS)
Outstanding—January 1, 2016		27,510			0.89		7.15
Issued		14,036			2.83
Exercised		(12,866	)		0.82
Forfeited		(1,170	)		0.82

Outstanding—December 31, 2016		27,510			1.91		7.75
Issued		5,614			1.55

Outstanding—December 31, 2017		33,124		$	1.91		6.75

Exercisable—December 31, 2017		27,510		$	1.91		6.75

Vested and expected to vest at December 31, 2017		27,510		$	1.91		6.74

Restricted Stock Awards for Employees For 2011 Plan

Restricted stock awards for employees for the 2011 Plan for the years ended December 31, 2016 and 2017 is as follows:


	SHARES
Outstanding—January 1, 2016		96,849
Granted		103,867
Vested		(99,898	)

Outstanding—December 31, 2016		101,118
Vested		(101,118	)

Outstanding—December 31, 2017		—

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs

The following table summarizes the reporting of total stock-based compensation expense resulting from employee and non-employee stock options:


	NINE MONTHS ENDED SEPTEMBER 30,
(in thousands)	2017		2018
Research and development	$	46	$	398
General and administrative		305		751

Total stock-based compensation	$	351	$	1,149

The following table summarizes the reporting of total stock-based compensation expense resulting from employee and non-employee stock options and restricted stock awards:


	YEARS ENDED DECEMBER 31,
(In thousands)	2016		2017
Research and development	$	78	$	62
General and administrative		462		437

Total stock-based compensation	$	540	$	499

Employee Stock Option [Member]

Share-based Compensation, Activity

Stock option activity for employee awards for the nine months ended September 30, 2018 was as follows:


	UNITS			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE CONTRACTUAL LIFE (YEARS)
Outstanding—January 1, 2018		1,946,230		$	1.66		8.70
Issued		1,167,077			12.13
Exercised		(181,884	)		1.42
Forfeited		(185,003	)		1.94

Outstanding—September 30, 2018		2,746,420		$	6.26		8.74

Exercisable—September 30, 2018		2,347,080		$	4.54		8.60

Vested and expected to vest at September 30, 2018		2,470,131		$	6.07		8.70


	UNITS			WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE CONTRACTUAL LIFE (YEARS)
Outstanding—January 1, 2018		33,125		$	1.91		6.75
Issued		—			—
Exercised		(26,337	)		2.17
Forfeited		—			—

Outstanding—September 30, 2018		6,788		$	1.09		4.89

Exercisable—September 30, 2018		6,737		$	1.09		4.89

Vested and expected to vest at September 30, 2018		6,737		$	1.09		4.89

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Company's Effective Income Tax Rate

A reconciliation of the expected income tax benefit computed using the federal statutory income tax rate of 34% to the Company’s effective income tax rate is as follows:


	DECEMBER 31,
(In thousands)	2016			2017
Income tax using the federal statutory tax rate	$	(4,491	)	$	(9,028	)
Impact of rate change		—			7,478
Research and development and orphan drug credit		(655	)		(517	)
Permanent adjustments to expenses		(3	)		76
Stock compensation		145			42
Prior year adjustment		—			(100	)
Changes in valuation allowance		5,004			2,049

Total income taxes	$	—		$	—

Schedule of Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and liabilities are as follows:


	DECEMBER 31,
(In thousands)	2016			2017
Deferred tax assets
Net operating losses	$	10,547		$	11,715
Research credits		1,462			2,045
Stock compensation		5			49
Other temporary differences		202			349
Valuation allowance		(12,157	)		(14,124	)

Total assets		59			34
Deferred tax liabilities
Fixed and intangible assets		(59	)		(34	)

Total liabilities		(59	)		(34	)

Net deferred tax assets	$	—		$	—

Fair Value Measurement (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation

The Company has determined that the warrant liabilities’ fair values are Level 3 items within the fair value hierarchy. The following table presents the changes in the warrant liabilities:


(in thousands)
Balance at December 31, 2017	$	93
Fair value of Term A Warrants issued under the Loan and Security Agreement		326
Fair value of Term B Warrants issued under the Loan and Security Agreement		686
Change in fair value of warrants		(63	)

Balance at September 30, 2018		1,042

The following table presents the changes in the warrant liabilities:


(In thousands)
Balance at January 1, 2016	$	180
Fair value of Series A warrants expired/exercised		(109	)
Changes in fair value of warrants		(24	)

Balance at December 31, 2016		47
Changes in fair value of warrants		46

Balance at December 31, 2017	$	93

Fair Value Measurements, Recurring and Nonrecurring

The following tables present the Company’s fair value hierarchy for those assets and liabilities measured at fair value as of December 31, 2017 and September 30, 2018:


(in thousands)	TOTAL AS OF DECEMBER 31, 2017		LEVEL 1		LEVEL 2		LEVEL 3
Current Assets
Money market funds ^(a)	$	39,124	$	39,124	$	—	$	—

Other current liabilities
Warrant liabilities	$	93	$	—	$	—	$	93


(in thousands)	TOTAL AS OF SEPTEMBER 30, 2018		LEVEL 1		LEVEL 2		LEVEL 3
Current Assets
Cash and cash equivalents:
Money market funds	$	72,746	$	72,746	$	—	$	—
Commercial paper		2,999		2,999		—		—

Total cash and cash equivalents	$	75,745	$	75,745	$	—	$	—

Short-term investments:
U.S. government securities	$	32,212	$	32,212	$	—	$	—
Corporate securities		12,156		—		12,156		—
Agency securities		10,928		—		10,928		—

Total short-term investments	$	55,296	$	32,212	$	23,084	$	—

Other current liabilities
Warrant liabilities	$	1,042	$	—	$	—	$	1,042

^(a)

The money market funds noted above are included in cash and cash equivalents.

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Long-term Debt (Tables)

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Schedule of Long-term Debt Instruments

The components of debt are as follows:


(in thousands)	DECEMBER 31, 2017		SEPTEMBER 30, 2018
Term A Loan	$	—	$	20,000
Term B Loan		—		15,000
Less unamortized deferred cost		—		(3,358	)

Long-term debt	$	—	$	31,642

Schedule of Maturities of Long-term Debt

The following table sets forth the Company’s future minimum principal payments (in thousands):


2018	$	—
2019		—
2020		9,000
2021		12,000
2022		12,000
2023		2,000

	$	35,000

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
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Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Warrants (Tables)

9 Months Ended

Sep. 30, 2018

Warrants [Abstract]

Schedule of Stockholders' Equity Note, Warrants or Rights

As of September 30, 2018, the following warrants were outstanding:


	OUTSTANDING SHARES		EXERCISE PRICE PER SHARE		EXPIRATION DATE
2014 Warrants		19,931	$	5.912		August 2020
Term A Warrants		53,720	$	11.169		February 2025
Term B Warrants		40,292	$	11.169		September 2025

		113,943

- Definition

Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable.

+ References + Details

Short-Term Investments (Tables)

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Debt Securities, Available-for-sale

The following table represents the Company’s available for sale short-term investments by major security type as of September 30, 2018:


(in thousands)	AMORTIZED COST		GROSS UNREALIZED LOSSES			TOTAL FAIR VALUE
Short-term investments:
Agency securities	$	10,938	$	(10	)	$	10,928
Corporate securities		12,166		(10	)		12,156
U.S. government securities		32,250		(38	)		32,212

Total short-term investments	$	55,354	$	(58	)	$	55,296

Organization and Nature of the Business - Narrative (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2018	Dec. 31, 2017	Sep. 30, 2018	Dec. 31, 2016
Retained Earnings (Accumulated Deficit)		$ (60,585)	$ (100,246)	$ (34,031)
Expected proceeds from issuance of debt		$ 35,000
Proceeds from Issuance of Preferred Stock, Preference Stock and Warrants	$ 4,400
Subsequent Event [Member] \| Series C Convertible Preferred Stock [Member]
Proceeds from Issuance of Preferred Stock, Preference Stock and Warrants	$ 4,400

Summary of Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2017
Lab equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, estimated useful life	5 years
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, estimated useful life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, estimated useful life	Lesser of useful life or lease term
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, estimated useful life	5 years
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, estimated useful life	5 years
Minimum [Member] \| Software [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, estimated useful life	3 years
Maximum [Member] \| Software [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, estimated useful life	5 years

Summary of Significant Accounting Policies - Narrative (Detail)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($) Segment shares	Dec. 31, 2016 USD ($)
Accounting Policies [Abstract]
Asset impairment charges			$ 48,000	$ 0
Number of operating segments \| Segment			1
Weighted-average number of common shares outstanding \| shares			11,459,683
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	34.00%
Re-measurement of tax	$ 7,478,000
Capitalized costs, initial public offering costs		$ 9,400,000

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Summary Of Significant Accounting Policies [Abstract]
Convertible preferred stock	0	10,954,012	11,439,752	8,263,377
Warrants	113,943	19,931	19,931	19,931
Vested and unvested stock options	2,753,208	1,902,997	1,979,306	508,328
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2,867,151	12,876,940	13,438,989	8,791,636

Summary of Significant Accounting Policies - Summary of Calculation of Unaudited Pro Forma Basic and Diluted Net Loss Per Common Share (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Numerator
Net loss attributable to common stockholders	$ (39,661)	$ (17,408)	$ (26,554)	$ (13,209)
Pro forma adjustments to eliminate changes in fair value of preferred stock warrant liability			46
Net loss used to compute pro forma net loss per share			$ (26,508)
Denominator
Weighted average of common shares outstanding			2,028,224

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, Gross		$ 1,228	$ 580
Less accumulated depreciation and amortization		(440)	(268)
Property and equipment, net	$ 1,826	788	312
Lab equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross		860	375
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross		128	103
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross		100	50
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross		78	26
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross		52	16
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross		$ 10	$ 10

Property and Equipment - Narrative (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 177,000	$ 116,000

Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Accrued Expenses [Abstract]
Accrued employee costs	$ 2,739	$ 1,581	$ 744
Accrued research costs	2,759	566	70
Accrued other costs	762	410	88
Accrued expenses	$ 6,260	$ 2,557	$ 902

Convertible Preferred Stock - Narrative (Detail) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended		12 Months Ended
	Feb. 28, 2018 USD ($) shares	Jun. 30, 2018 shares	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) $ / shares
Preferred Stock, Dividend Rate, Percentage			8.00%		8.00%
Reverse Stock Split, Conversion Ratio		1.78112
Public offering price per share					$ 16.74
Proceeds from issuance initial public offering \| $			$ 98,325	$ 0	$ 30,000
Preferred Stock, Shares Issued \| shares	707,680		0
Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants \| $	$ 4,400
Shares of common stock issued, after preferred stock conversion \| shares		11,837,073
Series A Convertible Preferred Stock [Member]
Temporary equity, liquidation price per share					$ 1.02
Series B Convertible Preferred Stock [Member]
Temporary equity, liquidation price per share					3.319
Series C Convertible Preferred Stock [Member]
Temporary equity, liquidation price per share					$ 6.2705

Warrants - Narrative (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Dec. 31, 2013
Class of Warrant or Right [Line Items]
Warrants outstanding	113,943	113,943	19,931	19,931	19,931
Change in fair value of warrants		$ (63)	$ 32	$ 46	$ (24)
Series A Convertible Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Preferred stock and warrants issued during the period, shares							69,000
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 1.02
Warrants outstanding					47,791
2014 Warrants [Member]
Class of Warrant or Right [Line Items]
Preferred stock and warrants issued during the period, shares						19,931
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 5.912	$ 5.912
Warrants outstanding	19,931	19,931
Investment warrants Expiration Date		Aug. 31, 2020
Change in fair value of warrants		$ (149)	$ (32)
Term A Warrants [Member]
Class of Warrant or Right [Line Items]
Preferred stock and warrants issued during the period, shares		53,720
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 11.169	$ 11.169
Warrants outstanding	53,720	53,720
Investment warrants Expiration Date		Feb. 28, 2025
Warrant coverage, equal to percent of principal borrowing amounts	3.00%	3.00%
Change in fair value of warrants		$ (131)
Term B Warrants [Member]
Class of Warrant or Right [Line Items]
Preferred stock and warrants issued during the period, shares	40,292
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 11.169	$ 11.169
Warrants outstanding	40,292	40,292
Investment warrants Expiration Date		Sep. 07, 2025
Change in fair value of warrants		$ 343
Series B Warrants [Member]
Class of Warrant or Right [Line Items]
Preferred stock and warrants issued during the period, shares						35,504
Warrants outstanding				35,504	35,504
Series B Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 3.319
Investment warrants Expiration Date				Aug. 31, 2020

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Operating Leases (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
2018	$ 49	$ 730
2019	84	859
2020	210	834
2021	219	1,123
2022	228	1,148
Thereafter	$ 524	701
Total minimum lease payments		$ 5,395

Commitments and Contingencies - Narrative (Detail) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Rent expense under operating leases	$ 841,000	$ 304,000	$ 526,000	$ 268,000
Remaining future minimum lease payments, 2018	49,000		730,000
Remaining future minimum lease payments, 2019	84,000		859,000
Remaining future minimum lease payments, 2020	210,000		834,000
Remaining future minimum lease payments, 2021	219,000		1,123,000
Remaining future minimum lease payments, 2022	228,000		1,148,000
Remaining future minimum lease payments, 2023 and thereafter	$ 524,000		701,000
Stable Liquid Glucagon [Member]
Loss Contingencies [Line Items]
Proceed from grant to help fund			760,000
Expected grant for development of liquid glucagon			872,000
Minimum required sale to meet original award amount			$ 750,000,000
Minimum required sale to meet original award, Description			If sales of glucagon for use in the artificial pancreas exceed $750 million in the first five years after the first commercial sale, then the Company would be required to make an additional payment equal to the original award amount
Exercise Induced Hypoglycemia [Member]
Loss Contingencies [Line Items]
Proceed from grant to help fund			$ 929,000
Minimum required sale to meet original award amount			$ 1,000,000,000
Minimum required sale to meet original award, Description			If sales exceed $1 billion, the Company will be required to make a milestone payment equal to two times the award amount
Annual royalty payments			$ 500,000
Type 1 Diabetes Chronic Glucagon [Member]
Loss Contingencies [Line Items]
Proceed from grant to help fund			1,004,000
Minimum required sale to meet original award amount			$ 500,000,000
Minimum required sale to meet original award, Description			For each chronic glucagon program where sales exceed $500 million, the Company will be required to pay an additional amount equal to two times the award amount
Annual royalty payments			$ 500,000
San Diego California [Member]
Loss Contingencies [Line Items]
Letter of credit, Outstanding Amount			$ 58,000

Shareholder Notes Receivables - Narrative (Detail) - Chief Executive Officer [Member] - USD ($) $ in Thousands	1 Months Ended
	Jan. 31, 2017	Nov. 30, 2014	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Receivables		$ 107
Notes Receivables, interest rate		1.93%
Note Receivable, allowance			$ 73
Note Receivable written off	$ 73

Stock Compensation Plan - Narrative (Detail) - USD ($)	9 Months Ended		12 Months Ended
Stock Compensation Plan - Narrative (Detail) - USD ($)	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2018	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options			$ 1,311,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 6 months 3 days		1 year 4 months 2 days
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 6,900,000
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value	$ 6.53		$ 0.94	$ 1.55
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 1,700,000		$ 1,258,000	$ 9,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value	$ 29,300,000		7,422,000	122,000
Non Employee Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	2 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, outstanding, Intrinsic Value	$ 111,000		110,000	8,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	111,000		111,000	8,000
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost	$ 114,000	$ 12,000	35,000	8,000
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value				157,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value			$ 0	$ 294,000
2011 Stock Option Issuance Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			336,866			4,714,982
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period			10 years
2011 Stock Option Issuance Plan [Member] \| Previously Reported [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized						4,378,116
2011 Stock Option Issuance Plan [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period			48 months
2011 Stock Option Issuance Plan [Member] \| Non Employee Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period			24 months
2018 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized					1,822,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,539,190

Stock Compensation Plan - Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Method Used (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Sharebased Compensation Arrangementby Sharebased Payment Award Fair Value Assumptions Method Used [Abstract]
Expected term	6 years	6 years 1 month 6 days	6 years 22 days	5 years 10 months 17 days
Expected volatility	58.55%	61.23%	61.10%	61.46%
Risk-free interest rate	2.80%	2.05%	2.06%	1.48%
Expected dividends	0.00%	0.00%	0.00%	0.00%

Stock Compensation Plan - Employee Stock Award Activity (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	1,979,306	508,328
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	2,753,208	1,979,306	508,328
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	1,946,230	480,838	364,612
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	1,167,077	1,642,565	138,115
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(181,884)	(117,318)	(12,538)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares	(185,003)	(13,256)	(9,350)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Expired, Number of Shares		(46,599)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	2,746,420	1,946,230	480,838	364,612
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	2,347,080	1,709,929
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	2,470,131	1,735,470
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 1.66	$ 1.69	$ 1.32
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	12.13	1.64	2.71
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	1.42	1.59	0.87
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	1.94	1.83
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price			1.23
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price		1.53
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	6.26	1.66	$ 1.69	$ 1.32
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	4.54	1.64
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 6.07	$ 1.66
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	8 years 8 months 26 days	8 years 8 months 12 days	6 years 8 months 15 days	6 years 3 months 29 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	8 years 7 months 6 days	8 years 8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	8 years 8 months 12 days	8 years 8 months 12 days
Non Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	33,124	27,510	27,510
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period		5,614	14,036
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period			(12,866)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares			(1,170)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number		33,124	27,510	27,510
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number		27,510
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number		27,510
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 1.91	$ 1.91	$ 0.89
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price		1.55	2.83
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price			0.82
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price			0.82
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price		1.91	$ 1.91	$ 0.89
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price		1.91
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price		$ 1.91
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term		6 years 9 months	7 years 9 months	7 years 1 month 24 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term		6 years 9 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term		6 years 8 months 26 days
Non Employee Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	33,125
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(26,337)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	6,788	33,125
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	6,737
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	6,737
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 1.91
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	2.17
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	1.09	$ 1.91
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	1.09
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 1.09
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	4 years 10 months 20 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	4 years 10 months 20 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	4 years 10 months 20 days

Stock Compensation Plan - Restricted Stock Award For Employees (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options [Abstract]
Restricted stock, Outstanding	101,118	96,849
Restricted stock, Granted		103,867
Restricted stock, Vested	(101,118)	(99,898)
Restricted stock, Outstanding		101,118

Stock Compensation Plan - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Allocated Share-based Compensation Expense	$ 1,149	$ 351	$ 499	$ 540
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Allocated Share-based Compensation Expense	398	46	62	78
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Allocated Share-based Compensation Expense	$ 751	$ 305	$ 437	$ 462

Income Taxes - Narrative (Detail) - USD ($)	9 Months Ended	12 Months Ended
Income Taxes - Narrative (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Income tax expense			$ 0	$ 0
Federal statutory income tax rate	21.00%		34.00%
Interest and penalties related to income taxes			$ 0	0
Federal net operating loss carryforwards			55,786,000	31,011,000
Federal research and orphan drug credit carryforwards			2,045,000	$ 1,462,000
Net reduction in deferred tax assets due to tax law change			7,478,000
Reduction in the valuation allowance due to tax law change			$ 7,478,000
Scenario, Plan [Member]
Income Tax Disclosure [Line Items]
Federal statutory income tax rate		21.00%
Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
NOLs and research and orphan drug credit carryforwards			2025
Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
NOLs and research and orphan drug credit carryforwards			2036

Income Taxes - Schedule of Effective Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax using the federal statutory tax rate	$ (9,028)	$ (4,491)
Impact of rate change	7,478	0
Research and development and orphan drug credit	(517)	(655)
Permanent adjustments to expenses	76	(3)
Stock compensation	42	145
Prior year adjustment	(100)	0
Changes in valuation allowance	2,049	5,004
Total income taxes	$ 0	$ 0

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets net
Net operating losses	$ 11,715	$ 10,547
Research credits	2,045	1,462
Stock compensation	49	5
Other temporary differences	349	202
Valuation allowance	(14,124)	(12,157)
Total assets	34	59
Deferred tax liabilities Fixed and intangible assets	(34)	(59)
Total liabilities	(34)	(59)
Net deferred tax assets	$ 0	$ 0

Related Party Transaction - Narrative (Detail)	12 Months Ended
Related Party Transaction - Narrative (Detail)	Dec. 31, 2017 USD ($)
Spouse of Officer [Member]
Related Party Transaction [Line Items]
Related party transaction paid for website debelopment	$ 37,000

Subsequent Events - Narrative (Detail) - USD ($)		1 Months Ended	9 Months Ended
Subsequent Events - Narrative (Detail) - USD ($)	Mar. 01, 2018	Feb. 28, 2018	Sep. 30, 2018	Mar. 31, 2018
Subsequent Event [Line Items]
Preferred Stock, Shares Issued		707,680	0
Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants		$ 4,400,000
Line of Credit Facility, Maximum Borrowing Capacity				$ 45,000,000
Debt Instrument, Face Amount			$ 35,000,000	$ 20,000,000
Proceeds from second tranche of the Loan and Security Agreement			15,000,000
Additional expected proceeds from third tranche of the Loan and Security Agreement			$ 10,000,000
Interest rate, thirty-day LIBOR plus stated percentage			6.75%
Period debt payments are interest only			24 months
Debt Instrument, Term			59 months
Prepayment allowed per debt agreement			$ 2,000,000
Final fee payment percentage			6.50%
Debt, non-utilization fee percentage			2.00%
Maximum [Member]
Subsequent Event [Line Items]
Principal payments on debt to begin			36 months
Minimum [Member]
Subsequent Event [Line Items]
Principal payments on debt to begin			24 months
Subsequent Event [Member]
Subsequent Event [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		45,000,000
Debt Instrument, Face Amount		$ 20,000,000
Proceeds from second tranche of the Loan and Security Agreement			$ 15,000,000
Additional expected proceeds from third tranche of the Loan and Security Agreement			$ 10,000,000
Interest rate, thirty-day LIBOR plus stated percentage		6.75%
Period debt payments are interest only		24 months
Debt Instrument, Term		59 months
Number of warrant issued	95,686
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 6.2705
Prepayment allowed per debt agreement		$ 2,000,000
Prepayment fee percentage		1.50%
Final fee payment percentage		6.50%
Debt, non-utilization fee percentage		2.00%
Subsequent Event [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Principal payments on debt to begin		36 months
Subsequent Event [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Principal payments on debt to begin		24 months
Subsequent Event [Member] \| Series C Convertible Preference Shares [Member]
Subsequent Event [Line Items]
Preferred Stock, Shares Issued		707,680
Preferred stock, value per share		$ 6.2705
Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants		$ 4,400,000
Subsequent Event [Member] \| Leased Space [Member]
Subsequent Event [Line Items]
Letter of credit		$ 85,000
Lease expiration date		Nov. 30, 2024

Subsequent Events - Schedule of Annual Minimum Lease Payments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Feb. 28, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
2019	$ 84		$ 859
2020	210		834
2021	219		1,123
2022	228		1,148
Thereafter	$ 524		701
Total minimum lease payments			$ 5,395
Subsequent Event [Member]
Subsequent Event [Line Items]
2018		$ 163
2019		202
2020		210
2021		219
2022		228
Thereafter		462
Total minimum lease payments		$ 1,484

Reverse Stock Split and Initial Public Offering - Narrative (Detail) $ / shares in Units, $ in Millions	3 Months Ended
	Jun. 30, 2018 USD ($) shares	Sep. 30, 2018 $ / shares shares	Jun. 25, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares
Reverse Stock Split and Initial Public Offering [Abstract]
Reverse Stock Split, Conversion Ratio	1.78112
Common Shares, Par Value Per Share \| $ / shares		$ 0.0001		$ 0.0001	$ 0.0001
Common Shares, Shares, Issued		20,755,666	6,555,000	2,159,068	1,927,237
Shares Issued, Price Per Share \| $ / shares			$ 15.00
Common shares issued, due to exercise of underwriter option			855,000
Net Proceeds from Issuance Initial Public Offering \| $	$ 89.0
Shares of common stock issued, after preferred stock conversion	11,837,073

Long-Term Debt - Narrative (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					$ 45,000
Debt Instrument, Face Amount	$ 35,000				$ 20,000
Proceeds from second tranche of the Loan and Security Agreement	15,000
Additional expected proceeds from third tranche of the Loan and Security Agreement	$ 10,000
Interest rate, thirty-day LIBOR plus stated percentage	6.75%
Debt Instrument, Interest Rate, Stated Percentage	8.86%
Period debt payments are interest only	24 months
Debt Instrument, Term	59 months
Prepayment allowed per debt agreement	$ 2,000
Prepayment penalty percentage	1.50%
Final payment fee percentage	6.50%
Debt, non-utilization fee percentage	2.00%
In event of default, additional percentage plus current rate penalty	5.00%
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ (3,358)
Long-term debt	31,642		$ 0
Debt Issuance Costs, Gross	3,700
Interest expense	(1,490)	$ (1)	$ (2)	$ (2)
Amortization of debt issuance costs	$ 312	$ 0
Maximum [Member]
Debt Instrument [Line Items]
Principal payments on debt to begin	36 months
Minimum [Member]
Debt Instrument [Line Items]
Principal payments on debt to begin	24 months
Term A Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 20,000
Term B Loan [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 15,000

Long-Term Debt - Future Principal Payments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Mar. 31, 2018
Debt Disclosure [Abstract]
Future principal payments, 2018	$ 0
Future principal payments, 2019	0
Future principal payments, 2020	9,000
Future principal payments, 2021	12,000
Future principal payments, 2022	12,000
Future principal payments, 2023	2,000
Long-term Debt	$ 35,000	$ 20,000

Warrants - Schedule of Stockholders' Equity Note, Warrants or Rights (Detail) - $ / shares	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Class of Warrant or Right [Line Items]
Warrants outstanding	113,943	19,931	19,931	19,931
2014 Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding	19,931
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 5.912
Investment warrants Expiration Date	Aug. 31, 2020
Term A Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding	53,720
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 11.169
Investment warrants Expiration Date	Feb. 28, 2025
Term B Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants outstanding	40,292
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 11.169
Investment warrants Expiration Date	Sep. 07, 2025

Fair Value Measurement - Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Detail) - USD ($)
$ in Thousands

9 Months Ended

12 Months Ended

Sep. 30, 2018

Sep. 30, 2017

Dec. 31, 2017

Dec. 31, 2016

Sep. 30, 2018

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Warrant liabilities

$ 93

$ 47

$ 180

Money market funds

$ 72,746

$ 39,124

^[1]

Commercial paper

2,999

Change in fair value of warrants

(63)

(24)

Cash and cash equivalents

45,914

75,745

42,045

$ 32,269

$ 44,487

Fair value of Series A warrants expired/exercised

(109)

Short-term Investments

55,296

Warrant liabilities

1,042

Warrants liabilities

1,042

$ 47

$ 180

1,042

$ 47

$ 180

Term A Warrants [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair value of Term A Warrants issued under the Loan and Security Agreement

326

Change in fair value of warrants

(131)

Term B Warrants [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair value of Term A Warrants issued under the Loan and Security Agreement

686

Change in fair value of warrants

343

Fair Value, Inputs, Level 1 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Warrant liabilities

Money market funds

72,746

39,124

^[1]

Commercial paper

2,999

Cash and cash equivalents

75,745

Short-term Investments

32,212

Warrant liabilities

Warrants liabilities

Fair Value, Inputs, Level 2 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Warrant liabilities

Money market funds

^[1]

Commercial paper

Cash and cash equivalents

Short-term Investments

23,084

Warrant liabilities

Warrants liabilities

Fair Value, Inputs, Level 3 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Warrant liabilities

Money market funds

^[1]

Commercial paper

Cash and cash equivalents

Short-term Investments

Warrant liabilities

1,042

Warrants liabilities

$ 1,042

$ 93

1,042

$ 93

US Treasury and Government [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

32,212

US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

32,212

US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

Corporate Debt Securities [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

12,156

Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

12,156

Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

Agency Securities [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

10,928

Agency Securities [Member] | Fair Value, Inputs, Level 1 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

Agency Securities [Member] | Fair Value, Inputs, Level 2 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

10,928

Agency Securities [Member] | Fair Value, Inputs, Level 3 [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Short-term Investments

$ 0

[1]	The money market funds noted above are included in cash and cash equivalents.

Short-Term Investments (Detail) - USD ($) $ in Thousands	3 Months Ended
Short-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available For Sale Securities Maturities Period	212 days
Available-for-sale Securities, Amortized Cost Basis	$ 55,354
Accumulated other comprehensive loss	(58)	$ 0
Short-term Investments	55,296	$ 0
Agency Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	10,938
Accumulated other comprehensive loss	(10)
Short-term Investments	10,928
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	12,166
Accumulated other comprehensive loss	(10)
Short-term Investments	12,156
US Treasury and Government [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	32,250
Accumulated other comprehensive loss	(38)
Short-term Investments	$ 32,212