Verrica Pharmaceuticals (VRCA) 10-Q 7 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 02, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	VRCA
Entity Registrant Name	Verrica Pharmaceuticals Inc.
Entity Central Index Key	1,660,334
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		25,696,371
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transaction Period	true

CONDENSED BALANCE SHEETS

CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 38,311	$ 8,663
Marketable securities	58,664
Prepaid expenses and other assets	1,702	420
Total current assets	98,677	9,083
Property, plant and equipment, net	114
Deposits	14
Total assets	98,805	9,083
Current liabilities:
Accounts payable	1,067	153
Accrued expenses	1,346	449
Accounts payable and accrued expenses - related party	38	14
Total current liabilities	2,451	616
Total liabilities	2,451	616
Commitments and Contingencies (Note 5)
Convertible preferred stock		15,508
Stockholders’ equity (deficit):
Preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding as of September 30, 2018 and December 31, 2017
Common stock, $0.0001 par value; 200,000,000 and 33,236,900 shares authorized as of September 30, 2018 and December 31, 2017, respectively; 25,801,515 shares issued and 25,696,371 shares outstanding as of September 30, 2018 and 3,804,643 shares issued and 3,699,499 shares outstanding as of December 31, 2017, respectively	3
Treasury stock, at cost, 105,144 shares as of September 30, 2018 and December 31, 2017	0	0
Additional paid-in capital	123,365	5,394
Accumulated deficit	(27,007)	(12,435)
Accumulated other comprehensive loss	(7)
Total stockholders’ equity (deficit)	96,354	(7,041)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 98,805	9,083
Series A Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock		10,508
Series B Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock		$ 5,000

CONDENSED BALANCE SHEETS (Paren

CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	33,236,900
Common stock, shares issued	25,801,515	3,804,643
Common stock, shares outstanding	25,696,371	3,699,499
Treasury stock, shares	105,144	105,144
Series A Convertible Preferred Stock [Member]
Convertible preferred stock, shares authorized	0	21,302,972
Convertible preferred stock, shares issued	0	21,302,972
Convertible preferred stock, shares outstanding	0	21,302,972
Series B Convertible Preferred Stock [Member]
Convertible preferred stock, shares authorized	0	1,937,984
Convertible preferred stock, shares issued	0	1,937,984
Convertible preferred stock, shares outstanding	0	1,937,984

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating expenses:
Research and development	$ 3,484	$ 1,120	$ 8,022	$ 2,612
General and administrative	3,681	238	7,170	411
Total operating expenses	7,165	1,358	15,192	3,023
Loss from operations	(7,165)	(1,358)	(15,192)	(3,023)
Other income (expense):
Interest income	427		621
Other expense	(1)		(1)
Interest expense - related party		(1)		(1)
Total other income (expense)	426	(1)	620	(1)
Net loss	$ (6,739)	$ (1,359)	$ (14,572)	$ (3,024)
Net loss per share, basic and diluted	$ (0.27)	$ (0.48)	$ (1.30)	$ (1.06)
Weighted average common shares outstanding, basic and diluted	24,847,512	2,850,640	11,230,401	2,850,143
Net loss	$ (6,739)	$ (1,359)	$ (14,572)	$ (3,024)
Other comprehensive loss:
Unrealized loss on marketable securities	(7)		(7)
Comprehensive loss	$ (6,746)	$ (1,359)	$ (14,579)	$ (3,024)

CONDENSED STATEMENTS OF CONVERT

CONDENSED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - 9 months ended Sep. 30, 2018 - 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 Deficit [Member]	Treasury Stock at Cost [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2017	$ (7,041)					$ 5,394	$ (12,435)
Beginning Balance (shares) at Dec. 31, 2017		21,302,972	1,937,984
Beginning Balance at Dec. 31, 2017	15,508	$ 10,508	$ 5,000
Beginning Balance (shares) at Dec. 31, 2017					3,804,643			105,144
Stock-based compensation	3,099					3,099
Series C convertible preferred stock				$ 21,000
Series C convertible preferred stock (shares)				4,606,267
Issuance costs for Series C preferred				$ (7)
Conversion of preferred stock into common stock	36,501	$ (10,508)	$ (5,000)	$ (20,993)	$ 2	36,499
Conversion of preferred stock into common stock (shares)		(21,302,972)	(1,937,984)	(4,606,267)	16,246,872
Issuance of common stock in connection with IPO, net of offering costs	78,374				$ 1	78,373
Issuance of common stock in connection with IPO, net of offering costs (shares)					5,750,000
Net loss	(14,572)						(14,572)
Unrealized loss on marketable securities	(7)								$ (7)
Ending Balance at Sep. 30, 2018	$ 96,354				$ 3	$ 123,365	$ (27,007)		$ (7)
Ending Balance (shares) at Sep. 30, 2018		0	0
Ending Balance (shares) at Sep. 30, 2018					25,801,515			105,144

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net loss	$ (14,572)	$ (3,024)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	3,099	3
Accretion of discounts on marketable securities	(47)
Depreciation expense	10
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,296)	(531)
Accounts payable	914	710
Accrued expenses	897	(22)
Accounts payable and accrued expenses - related party	24	128
Net cash used in operating activities	(10,971)	(2,736)
Cash flows from investing activities
Purchases of marketable securities	(58,624)
Purchases of property, plant and equipment	(124)
Net cash used in investing activities	(58,748)
Cash flows from financing activities
Proceeds from the issuance of common stock in connection with IPO	86,250
Net cash provided by financing activities	99,367	2,605
Net increase (decrease) in cash and cash equivalents	29,648	(131)
Cash and cash equivalents at the beginning of the period	8,663	527
Cash and cash equivalents at the end of the period	38,311	396
Supplemental disclosure of cash flow information:
Cash paid for interest		1
Supplemental disclosure of noncash investing and financing activities:
Conversion of preferred stock into common stock	36,501
IPO [Member]
Cash flows from financing activities
Payments of Stock Issuance Costs	(7,876)
Series A Convertible Preferred Stock [Member]
Cash flows from financing activities
Payments of Stock Issuance Costs		(95)
Proceeds received from subscription receivable / issuance of preferred stock		$ 2,700
Series C Convertible Preferred Stock [Member]
Cash flows from financing activities
Payments of Stock Issuance Costs	(7)
Proceeds received from subscription receivable / issuance of preferred stock	$ 21,000

Organization and Description of

Organization and Description of Business Operations	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business Operations	Note 1—Organization and Description of Business Operations Verrica Pharmaceuticals Inc. (the “Company”) was formed on July 3, 2013 and is incorporated in the State of Delaware. The Company is a clinical-stage medical dermatology company focused on identifying, developing and commercializing innovative pharmaceutical products for the treatment of skin diseases with significant unmet needs, with an initial focus on addressing molluscum contagiosum. Reverse Stock Split On June 4, 2018, the Company effected a 1.714-for-one reverse stock split of Company’s common stock. No fractional shares were issued in connection with the stock split. The par value and other terms of the common stock were not affected by the stock split. All share and per share amounts, including stock options, have been retroactively adjusted in these condensed financial statements for all periods presented to reflect the 1.714-for-one reverse stock split. Further, exercise prices of stock options have been retroactively adjusted in these condensed financial statements for all periods presented to reflect the 1.714-for-one reverse stock split. The number of shares of the Company’s preferred stock were not affected by the reverse stock split; however, the conversion ratios were adjusted to reflect the reverse stock split. Liquidity and Capital Resources The Company has incurred substantial operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As of September 30, 2018, the Company had an accumulated deficit of $27.0 million. On February 20, 2018 and March 7, 2018, the Company issued an aggregate of 4,606,267 shares of Series C convertible preferred stock, at an issuance price of $4.559 per share, for gross proceeds of $21.0 million. On June 19, 2018, the Company completed an initial public offering (“IPO”) of its common stock, which resulted in the issuance and sale of 5,750,000 shares of its common stock at a public offering price of $15.00 per share, generating net proceeds of $78.4 million after deducting underwriting discounts and other offering costs. Upon the closing of the IPO, all outstanding shares of the Company’s Series A, Series B and Series C convertible preferred stock were automatically converted into 16,246,872 shares of the Company’s common stock. In addition, upon the closing of the IPO, the Company’s amended and restated certificate of incorporation authorized the Company to issue up to 200,000,000 shares of common stock, $0.0001 par value per share, and 10,000,000 shares of preferred stock, $0.0001 par value per share, all of which shares of preferred stock will be undesignated.

Significant Accounting Policies

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Significant Accounting Policies	Note 2—Significant Accounting Policies Basis of Presentation The accompanying unaudited interim condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) as determined by Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, the unaudited interim condensed financial statements reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the balances and results for the periods presented. They may not include all of the information and footnotes required by GAAP for complete financial statements. Therefore, these financial statements should be read in conjunction with the Company’s audited financial statements and notes thereto for the year ended December 31, 2017 included in the Company’s final prospectus for its IPO dated as of June 14, 2018 and filed with the Securities and Exchange Commission (the “SEC”) on June 15, 2018 pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended. The results of operations for any interim periods are not necessarily indicative of the results that may be expected for the entire fiscal year or any other interim period. 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 and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates in the Company’s financial statements relate to the valuation of common stock and stock options. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially and adversely from these estimates. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected. 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 in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment. Cash, Cash Equivalents and Marketable Securities The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and money market mutual funds. The Company classifies its marketable securities as “available-for-sale”, pursuant to ASC 320 Investments—Debt and Equity Securities There were no marketable securities with a maturity of greater than one year as of September 30, 2018. The following table presents the Company’s marketable securities as of September 30, 2018 (in thousands): September 30, 2018 Amortized Gross Unrealized Gross Unrealized Fair Cost Gains Losses Value Commercial paper $ 34,569 $ — $ (1 ) $ 34,568 U.S. treasury securities 12,702 — (1 ) 12,701 Asset-backed securities 11,400 — (5 ) 11,395 Total marketable securities $ 58,671 $ — $ (7 ) $ 58,664 Concentrations of Credit Risk and Off-Balance Sheet Risk Cash, cash equivalents and marketable securities are financial instruments that are potentially subject to concentrations of credit risk. The Company’s deposits are in accounts at large financial institutions, and amounts may exceed federally insured limits. The Company believes it is not exposed to significant credit risk due to the financial strength of the depository institutions in which the funds are held. The Company has no financial instruments with off-balance sheet risk of loss. Research and Development Costs The Company’s research and development expenses consist primarily of costs associated with the Company’s clinical trials, salaries, payroll taxes, employee benefits, and equity-based compensation charges for those individuals involved in ongoing research and development efforts. Research and development costs are expensed as incurred. Advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. Fair Value Measurement ASC 820, Fair Value Measurements The accounting guidance classifies fair value measurements in one of the following three categories for disclosure purposes: Level 1: Quoted prices in active markets for identical assets or liabilities. Level 2: Inputs other than Level 1 prices for similar assets or liabilities that are directly or indirectly observable in the marketplace. Level 3: Unobservable inputs which are supported by little or no market activity and values determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant judgment or estimation. The following table presents fair value of the Company’s marketable securities as of September 30, 2018 (in thousands): Fair Value Measurement as of September 30, 2018 Level 1 Level 2 Level 3 Total Assets Commercial paper $ — $ 34,568 $ — $ 34,568 U.S. treasury securities 12,701 — — 12,701 Asset-backed securities — 11,395 — 11,395 Total assets $ 12,701 $ 45,963 $ — $ 58,664 Stock-Based Compensation The Company expenses stock-based compensation to employees and board members over the requisite service period based on the estimated grant-date fair value of the awards. The Company accounts for forfeitures as they occur. Stock-based awards with graded-vesting schedules are recognized on a straight-line basis over the requisite service period for each separately vesting portion of the award. The Company estimates the fair value of stock option grants using the Black-Scholes option-pricing model, and the assumptions used in calculating the fair value of stock-based awards represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment. All stock-based compensation costs are recorded in general and administrative or research and development costs in the statements of operations based upon the underlying individual’s role at the Company. Stock-based compensation for non-employee stock options is recorded over the vesting period and remeasured at fair value until they vest. Income Taxes Income taxes are recorded in accordance with ASC 740, Income Taxes 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 would more likely than not be realized assuming examination by the taxing authority. 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. The Company recognizes any interest and penalties accrued related to unrecognized tax benefits as income tax expense. Net Loss Per Share Net loss per share of common stock is computed by dividing net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss per share excludes the potential impact of Series A, Series B and Series C Preferred Stock, common stock options and unvested shares of restricted stock because their effect would be anti-dilutive due to the Company’s net loss. Since the Company had a net loss in each of the periods presented, basic and diluted net loss per common share are the same. The table below provides potential shares outstanding that were not included in the computation of diluted net loss per common share, as the inclusion of these securities would have been anti-dilutive: As of September 30, 2018 2017 Shares issuable upon conversion of Series A Preferred — 12,428,773 Shares issuable upon exercise of stock options 1,507,268 90,429 Non-vested shares under restricted stock grants 848,859 848,859 Recently Adopted Accounting Pronouncements In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Leases (Topic 842): Targeted Improvements In June 2018, the FASB issued ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting Revenue from Contracts with Customers In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework–Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU 2018-15, Intangibles–Goodwill and Other–Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Note 3—Related Party Transactions Prior to the IPO, the Company was controlled by PBM VP Holdings, LLC (“PBM VP Holdings”), an affiliate of PBM Capital Group, LLC. Paul B. Manning, who is the President and Chief Executive Officer of PBM Capital Group, LLC and the current chairman of the Company’s Board of Directors (the “Board”), and certain entities affiliated with Mr. Manning, continue to be the Company’s largest shareholder on a collective basis. On December 2, 2015, the Company entered into a Services Agreement (a “SA”) with PBM Capital Group, LLC. Pursuant to the terms of the SA, which had an initial term of twelve months (and was automatically renewable for successive monthly periods), PBM Capital Group, LLC rendered advisory and consulting services to the Company. Services provided under the SA included certain business development, operations, technical, contract, accounting and back office support services. In consideration for these services, the Company was obligated to pay PBM Capital Group, LLC a monthly management fee of $2,500. On March 29, 2018, the Company amended the SA with PBM Capital Group, LLC, effective as of April 1, 2018. Pursuant to the terms of the SA, as amended, which has an initial term of twelve months (and is automatically renewable for successive monthly periods), PBM Capital Group, LLC will render advisory and consulting services to the Company. Services provided under the SA may include certain business development, operations, technical, contract, accounting and back office support services. In consideration for these services, the Company is obligated to pay PBM Capital Group, LLC a monthly management fee of $50,000. The SA, as amended, provides for the termination by the Company with 30 days advance notice or a mutually agreed upon effective date for transition as individual services are cancelled with a corresponding reduction in the monthly management fee. For the three months ended September 30, 2018 and 2017, the Company incurred expenses under the SA of $150,000 and $7,500, respectively, which were primarily included in general and administrative expenses. For the nine months ended September 30, 2018 and 2017, the Company incurred expenses under the SA of $307,500 and $22,500, respectively, which were primarily included in general and administrative expenses. As of September 30, 2018 and December 31, 2017, the Company had a payable due to PBM Capital Group, LLC and its affiliates of $38,000 and $14,000, respectively. These balances include amounts due for other miscellaneous expenses incurred by PBM Capital Group, LLC and its affiliates.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Accrued Expenses	Note 4—Accrued Expenses Accrued expenses consisted of the following (in thousands): As of September 30, 2018 As of December 31, 2017 Compensation and related costs $ 855 $ 49 Clinical trials and drug development 83 233 Consulting - former Chief Scientific Officer 282 — Professional fees 26 129 Other 100 38 Total accrued expenses $ 1,346 $ 449

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 5—Commitments and Contingencies Litigation As of September 30, 2018 and December 31, 2017, there was no litigation against the Company. Supply Agreement and Purchase Order On March 22, 2018, the Company executed a purchase order with a supplier, denominated in Chinese yuan, pursuant to which the Company agreed to purchase approximately $2.3 million of crude cantharidin material. As of September 30, 2018, the Company purchased approximately $0.5 million of crude cantharidin material under this purchase order. On July 16, 2018, the Company entered into a supply agreement with the supplier. The executed purchase order is covered under the terms of the supply agreement. Pursuant to the supply agreement, the supplier has agreed that it will not supply cantharidin, any beetles or other raw material from which cantharidin is derived to any other customer in North America, subject to specified minimum annual purchase orders and forecasts. The supply agreement has an initial five-year term, which is subject to automatic renewal absent termination by either party in accordance with the terms of the supply agreement. Each party also has the right to terminate the supply agreement for other customary reasons such as material breach or bankruptcy. Agreements with Former Chief Scientific Officer On May 31, 2018, the Company and the former Chief Scientific Officer (“CSO”) executed a transition agreement to resign from employment as well as a Consulting Agreement (the “Consulting Agreement”) that began upon the closing of the IPO. The Consulting Agreement provides for cash payments to the former CSO of $29,375 per month for the first 12 months of the agreement. After the first 12 months, the former CSO will receive $300 per hour for each hour of consulting services provided. As of September 30, 2018, $0.3 million was accrued under this Consulting Agreement.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Stockholders' Equity	Note 6—Stockholders’ Equity Common Stock The Company has authorized 200,000,000 and 33,236,900 shares of common stock, $0.0001 par value per share, as of September 30, 2018 and December 31, 2017, respectively. Each share of common stock is entitled to one voting right. Common stock owners are entitled to dividends when funds are legally available and declared by the Board. On June 19, 2018, the Company completed an IPO of its common stock, which resulted in the issuance and sale of 5,750,000 shares of its common stock at a public offering price of $15.00 per share, generating net proceeds of $78.4 million after deducting underwriting discounts and other offering costs. The shares commenced trading on the Nasdaq Global Market on June 15, 2018 under the ticker symbol “VRCA.” Restricted Stock Pursuant to an Amended and Restated Stock Purchase Agreement (the “Amended and Restated Agreement”) between the Company and the former CSO, 848,859 shares held by the former CSO are subject to repurchase at $0.0001 per share. These shares will be released from the repurchase option on the earliest to occur of (i) a change in control, (ii) regulatory approval of the Company’s new drug application for cantharidin, (iii) commercial sale of products and (iv) a covered termination, as defined in the Amended and Restated Agreement. Convertible Preferred Stock On December 2, 2015, the Company issued an aggregate of 21,302,972 shares of Series A Preferred Stock to fourteen investors for cash consideration of $1.9 million, conversion of previously outstanding notes payable and accrued interest of $0.5 million and a stock subscription receivable of $8.5 million. The Company incurred aggregate issuance costs of $0.4 million, related to the issuance of the Series A Preferred Stock and subsequent settlement of the stock subscription receivable. PBM VP Holdings paid the Company $0.5 million during the year ended December 31, 2016, and $8.0 million during the year ended December 31, 2017 to settle the stock subscription receivable. Upon the closing of the IPO on June 19, 2018, all outstanding shares of the Company’s Series A Preferred Stock were automatically converted into 12,428,773 shares of the Company’s common stock. On December 15, 2017, the Company issued and sold an aggregate of 1,937,984 shares of Series B Preferred Stock, at an issuance price of $2.58 per share, for gross proceeds of $5.0 million. The Company did not incur any issuance costs for the Series B Preferred Stock. Upon the closing of the IPO on June 19, 2018, all outstanding shares of the Company’s Series B Preferred Stock were automatically converted into 1,130,679 shares of the Company’s common stock. On February 20, 2018 and March 7, 2018, the Company issued and sold an aggregate of 4,606,267 shares of Series C Preferred Stock, at an issuance price of $4.559 per share, for aggregate gross proceeds of $21.0 million. Upon the closing of the IPO on June 19, 2018, all outstanding shares of the Company’s Series C Preferred Stock were automatically converted into 2,687,420 shares of the Company’s common stock. The Company classified its Convertible Preferred Stock outside of stockholders’ deficit because redemption of the Convertible Preferred Stock, upon a deemed liquidation event, was not solely within the Company’s control.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	Note 7—Stock-Based Compensation In June 2018, the Board adopted and approved the 2018 Equity Incentive Plan (the “IPO Plan”), which amended and restated the Company’s prior 2013 Equity Incentive Plan (the “2013 Plan”) and became effective in connection with the IPO pricing on June 19, 2018. Prior to the effectiveness of the IPO Plan, the 2013 Plan provided for the grant of share-based awards to employees, directors and consultants of the Company. As a result of the effectiveness of the IPO Plan, no further grants may be made under the 2013 Plan. The IPO Plan provides for the grant of incentive stock options to employees, and for the grant of nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance-based stock awards and other forms of stock awards to employees, including officers, consultants and directors. The IPO Plan also provides for the grant of performance-based cash awards to employees, including officers, consultants and directors. The Company has initially reserved 3,738,199 shares of common stock for issuance under the IPO Plan, which is the sum of (1) 2,198,198 new shares, plus (2) the number of shares reserved for issuance under the 2013 Plan at the time the IPO Plan became effective, plus (3) any shares subject to outstanding stock options or other stock awards that would have otherwise returned to the 2013 Plan (such as upon the expiration or termination of a stock award prior to exercise). The number of shares of common stock reserved for issuance under the IPO Plan will automatically increase on January 1 each year, for a period of ten years, from January 1, 2019 through January 1, 2028, by 4% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Board. As of September 30, 2018, 1,989,033 shares were available for grant under the IPO Plan. Stock Options The Company’s employee stock options generally vest as follows: 25% after 12 months of continuous services and the remaining 75% on a ratable basis over a 36-month period from 12 months after the grant date. Stock options granted during the nine months ended September 30, 2018 have a maximum contractual term of 10 years. The stock options are subject to time vesting requirements through 2022, are nontransferable, and have term expiration dates set to expire through 2028. The fair value of each employee and non-employee stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies. Due to the lack of historical exercise history, the expected term of the Company’s stock options for employees has been determined utilizing the “simplified” method for awards. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. Prior to the Company’s IPO, in order to determine the fair value, the Company considered, among other things, contemporaneous valuations of the Company’s common stock, the Company’s business, financial condition and results of operations, including related industry trends affecting its operations; the likelihood of achieving a liquidity event, such as an initial public offering, or IPO, or sale, given prevailing market conditions; the lack of marketability of the Company’s common stock; the market performance of comparable publicly traded companies; and U.S. and global economic and capital market conditions. The grant date fair value of employee stock option awards is determined using the Black-Scholes option-pricing model. The following assumptions were used during the three and nine months ended September 30, 2018 and 2017 to estimate the fair value of employee stock option awards: For the Three Months Ended September 30, For the Nine Months Ended September 30, 2018 2017* 2018 2017 Exercise price $14.36 - $16.32 — $6.52 - $16.32 $0.90 Risk-free rate of interest 2.80% - 3.03% — 2.58% - 3.03% 1.92% - 2.23% Expected term (years) 6.19 — 6.13 6.25 Expected stock price volatility 79.31% - 83.18% — 70.58% - 83.67% 79.02% - 79.12% Weighted average estimated fair value share price $10.90 — $6.91 $0.12 Dividend yield — — — — * The Company did not grant stock options during the three months ended September 30, 2017. Non-employee options are remeasured to fair value each period through operations using a Black-Scholes option-pricing model until the options vest. There were no stock options granted to non-employees during the three and nine months ended September 30, 2018 and 2017. Key assumptions used to estimate the fair value of the non-employee stock options measured during the three and nine months ended September 30, 2018 and 2017 are as follows: For the Three Months Ended September 30, For the Nine Months Ended September 30, 2018 2017 2018 2017 Exercise price $0.90 $0.90 $0.90 $0.90 Risk-free rate of interest 2.81% - 3.01% 2.16% - 2.33% 2.33% - 3.01% 2.16% - 2.48% Expected term (years) 7.54 8.54 7.67 8.61 Expected stock price volatility 79.34% - 83.81% 77.92% - 78.84% 68.98% - 83.81% 77.92% - 79.12% Weighted average share price $15.78 $0.15 $13.92 $0.15 Dividend yield — — — — The following table summarizes the Company’s employee stock option activity under the 2013 Plan and the IPO Plan for the nine months ended September 30, 2018: Weighted average Weighted average remaining contractual Aggregate intrinsic Number of shares exercise price life (in years) value Outstanding as of December 31, 2017 17,502 $ 0.90 Options granted 1,416,839 8.31 Outstanding as of September 30, 2018 1,434,341 $ 8.22 9.4 $ 11,517,050 Options vested and exercisable as of September 30, 2018 7,294 $ 0.90 8.3 $ 111,963 The following table summarizes the Company’s non-employee stock option activity under the 2013 Plan and the IPO Plan for the nine months ended September 30, 2018: Weighted average Weighted average remaining contractual Aggregate intrinsic Number of shares exercise price life (in years) value Outstanding as of December 31, 2017 72,927 $ 0.90 Options granted — — Outstanding as of September 30, 2018 72,927 $ 0.90 7.5 $ 1,119,429 Options vested and exercisable as of September 30, 2018 52,265 $ 0.90 7.5 $ 802,268 The aggregate intrinsic value in the above table is calculated as the difference between fair value of the Company’s common stock price and the exercise price of the stock options. The weighted average grant date fair value per share for the employee stock option grants during the nine months ended September 30, 2018 and 2017 was $6.91 and $0.12, respectively. As of September 30, 2018, the total unrecognized compensation related to unvested employee and non-employee stock option awards granted was $7.0 million, which the Company expects to recognize over a weighted-average period of 1.5 years. Restricted Stock The following table summarizes restricted stock award activities for the nine months ended September 30, 2018: Weighted Average Grant Date Fair Number of Shares Value Nonvested at December 31, 2017 848,859 $ 0.33 Granted — — Nonvested at September 30, 2018 848,859 $ 0.33 As of September 30, 2018, the total unrecognized compensation expense related to the nonvested shares was $0.3 million. No compensation expense has been recognized for these nonvested shares as these shares are performance-based and the triggering event was not determined to be probable as of September 30, 2018. Stock-based compensation expense, which includes expense for both employees and non-employees, has been reported in the Company’s condensed statements of operations for the three and nine months ended September 30, 2018 and 2017 as follows (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2018 2017 2018 2017 Research and development $ 40 $ — $ 507 $ 3 General and administrative 1,476 — 2,592 — Total stock-based compensation $ 1,516 $ — $ 3,099 $ 3

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“GAAP”) as determined by Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, the unaudited interim condensed financial statements reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the balances and results for the periods presented. They may not include all of the information and footnotes required by GAAP for complete financial statements. Therefore, these financial statements should be read in conjunction with the Company’s audited financial statements and notes thereto for the year ended December 31, 2017 included in the Company’s final prospectus for its IPO dated as of June 14, 2018 and filed with the Securities and Exchange Commission (the “SEC”) on June 15, 2018 pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended. The results of operations for any interim periods are not necessarily indicative of the results that may be expected for the entire fiscal year or any other interim period.
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 and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates in the Company’s financial statements relate to the valuation of common stock and stock options. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially and adversely from these estimates. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected.
Segments	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 in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.
Cash, Cash Equivalents and Marketable Securities	Cash, Cash Equivalents and Marketable Securities The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and money market mutual funds. The Company classifies its marketable securities as “available-for-sale”, pursuant to ASC 320 Investments—Debt and Equity Securities There were no marketable securities with a maturity of greater than one year as of September 30, 2018. The following table presents the Company’s marketable securities as of September 30, 2018 (in thousands): September 30, 2018 Amortized Gross Unrealized Gross Unrealized Fair Cost Gains Losses Value Commercial paper $ 34,569 $ — $ (1 ) $ 34,568 U.S. treasury securities 12,702 — (1 ) 12,701 Asset-backed securities 11,400 — (5 ) 11,395 Total marketable securities $ 58,671 $ — $ (7 ) $ 58,664
Concentrations of Credit Risk and Off-Balance Sheet Risk	Concentrations of Credit Risk and Off-Balance Sheet Risk Cash, cash equivalents and marketable securities are financial instruments that are potentially subject to concentrations of credit risk. The Company’s deposits are in accounts at large financial institutions, and amounts may exceed federally insured limits. The Company believes it is not exposed to significant credit risk due to the financial strength of the depository institutions in which the funds are held. The Company has no financial instruments with off-balance sheet risk of loss.
Research and Development Costs	Research and Development Costs The Company’s research and development expenses consist primarily of costs associated with the Company’s clinical trials, salaries, payroll taxes, employee benefits, and equity-based compensation charges for those individuals involved in ongoing research and development efforts. Research and development costs are expensed as incurred. Advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made.
Fair Value Measurement	Fair Value Measurement ASC 820, Fair Value Measurements The accounting guidance classifies fair value measurements in one of the following three categories for disclosure purposes: Level 1: Quoted prices in active markets for identical assets or liabilities. Level 2: Inputs other than Level 1 prices for similar assets or liabilities that are directly or indirectly observable in the marketplace. Level 3: Unobservable inputs which are supported by little or no market activity and values determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant judgment or estimation. The following table presents fair value of the Company’s marketable securities as of September 30, 2018 (in thousands): Fair Value Measurement as of September 30, 2018 Level 1 Level 2 Level 3 Total Assets Commercial paper $ — $ 34,568 $ — $ 34,568 U.S. treasury securities 12,701 — — 12,701 Asset-backed securities — 11,395 — 11,395 Total assets $ 12,701 $ 45,963 $ — $ 58,664
Stock-Based Compensation	Stock-Based Compensation The Company expenses stock-based compensation to employees and board members over the requisite service period based on the estimated grant-date fair value of the awards. The Company accounts for forfeitures as they occur. Stock-based awards with graded-vesting schedules are recognized on a straight-line basis over the requisite service period for each separately vesting portion of the award. The Company estimates the fair value of stock option grants using the Black-Scholes option-pricing model, and the assumptions used in calculating the fair value of stock-based awards represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment. All stock-based compensation costs are recorded in general and administrative or research and development costs in the statements of operations based upon the underlying individual’s role at the Company. Stock-based compensation for non-employee stock options is recorded over the vesting period and remeasured at fair value until they vest.
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC 740, Income Taxes 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 would more likely than not be realized assuming examination by the taxing authority. 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. The Company recognizes any interest and penalties accrued related to unrecognized tax benefits as income tax expense.
Net Loss Per Share	Net Loss Per Share Net loss per share of common stock is computed by dividing net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss per share excludes the potential impact of Series A, Series B and Series C Preferred Stock, common stock options and unvested shares of restricted stock because their effect would be anti-dilutive due to the Company’s net loss. Since the Company had a net loss in each of the periods presented, basic and diluted net loss per common share are the same. The table below provides potential shares outstanding that were not included in the computation of diluted net loss per common share, as the inclusion of these securities would have been anti-dilutive: As of September 30, 2018 2017 Shares issuable upon conversion of Series A Preferred — 12,428,773 Shares issuable upon exercise of stock options 1,507,268 90,429 Non-vested shares under restricted stock grants 848,859 848,859
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Leases (Topic 842): Targeted Improvements In June 2018, the FASB issued ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting Revenue from Contracts with Customers In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework–Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU 2018-15, Intangibles–Goodwill and Other–Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Schedule of Marketable Securities	The following table presents the Company’s marketable securities as of September 30, 2018 (in thousands): September 30, 2018 Amortized Gross Unrealized Gross Unrealized Fair Cost Gains Losses Value Commercial paper $ 34,569 $ — $ (1 ) $ 34,568 U.S. treasury securities 12,702 — (1 ) 12,701 Asset-backed securities 11,400 — (5 ) 11,395 Total marketable securities $ 58,671 $ — $ (7 ) $ 58,664
Schedule of Fair Value of Marketable Securities	The following table presents fair value of the Company’s marketable securities as of September 30, 2018 (in thousands): Fair Value Measurement as of September 30, 2018 Level 1 Level 2 Level 3 Total Assets Commercial paper $ — $ 34,568 $ — $ 34,568 U.S. treasury securities 12,701 — — 12,701 Asset-backed securities — 11,395 — 11,395 Total assets $ 12,701 $ 45,963 $ — $ 58,664
Schedule of Potential Shares Outstanding Excluded in Computation of Diluted Net Loss Per Common Share	The table below provides potential shares outstanding that were not included in the computation of diluted net loss per common share, as the inclusion of these securities would have been anti-dilutive: As of September 30, 2018 2017 Shares issuable upon conversion of Series A Preferred — 12,428,773 Shares issuable upon exercise of stock options 1,507,268 90,429 Non-vested shares under restricted stock grants 848,859 848,859

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Accrued Expenses	Accrued expenses consisted of the following (in thousands): As of September 30, 2018 As of December 31, 2017 Compensation and related costs $ 855 $ 49 Clinical trials and drug development 83 233 Consulting - former Chief Scientific Officer 282 — Professional fees 26 129 Other 100 38 Total accrued expenses $ 1,346 $ 449

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2018
Schedule of Restricted Stock Awards Activities	The following table summarizes restricted stock award activities for the nine months ended September 30, 2018: Weighted Average Grant Date Fair Number of Shares Value Nonvested at December 31, 2017 848,859 $ 0.33 Granted — — Nonvested at September 30, 2018 848,859 $ 0.33
Schedule of Stock Based Compensation Expense	Stock-based compensation expense, which includes expense for both employees and non-employees, has been reported in the Company’s condensed statements of operations for the three and nine months ended September 30, 2018 and 2017 as follows (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2018 2017 2018 2017 Research and development $ 40 $ — $ 507 $ 3 General and administrative 1,476 — 2,592 — Total stock-based compensation $ 1,516 $ — $ 3,099 $ 3
Employee Stock Options [Member]
Assumptions Used to Estimate Fair Value	The grant date fair value of employee stock option awards is determined using the Black-Scholes option-pricing model. The following assumptions were used during the three and nine months ended September 30, 2018 and 2017 to estimate the fair value of employee stock option awards: For the Three Months Ended September 30, For the Nine Months Ended September 30, 2018 2017* 2018 2017 Exercise price $14.36 - $16.32 — $6.52 - $16.32 $0.90 Risk-free rate of interest 2.80% - 3.03% — 2.58% - 3.03% 1.92% - 2.23% Expected term (years) 6.19 — 6.13 6.25 Expected stock price volatility 79.31% - 83.18% — 70.58% - 83.67% 79.02% - 79.12% Weighted average estimated fair value share price $10.90 — $6.91 $0.12 Dividend yield — — — — * The Company did not grant stock options during the three months ended September 30, 2017.
Schedule of Stock Option Activity	The following table summarizes the Company’s employee stock option activity under the 2013 Plan and the IPO Plan for the nine months ended September 30, 2018: Weighted average Weighted average remaining contractual Aggregate intrinsic Number of shares exercise price life (in years) value Outstanding as of December 31, 2017 17,502 $ 0.90 Options granted 1,416,839 8.31 Outstanding as of September 30, 2018 1,434,341 $ 8.22 9.4 $ 11,517,050 Options vested and exercisable as of September 30, 2018 7,294 $ 0.90 8.3 $ 111,963
Non-Employee Stock Option [Member]
Assumptions Used to Estimate Fair Value	Key assumptions used to estimate the fair value of the non-employee stock options measured during the three and nine months ended September 30, 2018 and 2017 are as follows: For the Three Months Ended September 30, For the Nine Months Ended September 30, 2018 2017 2018 2017 Exercise price $0.90 $0.90 $0.90 $0.90 Risk-free rate of interest 2.81% - 3.01% 2.16% - 2.33% 2.33% - 3.01% 2.16% - 2.48% Expected term (years) 7.54 8.54 7.67 8.61 Expected stock price volatility 79.34% - 83.81% 77.92% - 78.84% 68.98% - 83.81% 77.92% - 79.12% Weighted average share price $15.78 $0.15 $13.92 $0.15 Dividend yield — — — —
Schedule of Stock Option Activity	The following table summarizes the Company’s non-employee stock option activity under the 2013 Plan and the IPO Plan for the nine months ended September 30, 2018: Weighted average Weighted average remaining contractual Aggregate intrinsic Number of shares exercise price life (in years) value Outstanding as of December 31, 2017 72,927 $ 0.90 Options granted — — Outstanding as of September 30, 2018 72,927 $ 0.90 7.5 $ 1,119,429 Options vested and exercisable as of September 30, 2018 52,265 $ 0.90 7.5 $ 802,268

Organization and Description _2

Organization and Description of Business Operations - Additional Information (Detail) $ / shares in Units, $ in Thousands	Jun. 19, 2018USD ($)$ / sharesshares	Jun. 04, 2018shares	Mar. 07, 2018USD ($)$ / sharesshares	Feb. 20, 2018USD ($)$ / sharesshares	Sep. 30, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares
Description Of Business [Line Items]
Stock split conversion ratio		1.714
Stock split description					No fractional shares were issued in connection with the stock split.
Number of fractional shares issued		0
Accumulated deficit | $					$ (27,007)	$ (12,435)
Issuance of common stock in connection with IPO, net of offering costs | $					$ 86,250
Common stock, authorized	200,000,000				200,000,000	33,236,900
Common stock, par value | $ / shares	$ 0.0001				$ 0.0001	$ 0.0001
Preferred stock, authorized	10,000,000				10,000,000	10,000,000
Preferred stock, par value | $ / shares	$ 0.0001				$ 0.0001	$ 0.0001
IPO [Member]
Description Of Business [Line Items]
Convertible preferred stock share issued	5,750,000				2,198,198
Public offering price of common stock | $ / shares	$ 15
Issuance of common stock in connection with IPO, net of offering costs | $	$ 78,400
Conversion of preferred stock into common stock, shares	16,246,872
Series C Convertible Preferred Stock [Member]
Description Of Business [Line Items]
Convertible preferred stock share issued			4,606,267	4,606,267
Convertible preferred stock share issued price per share | $ / shares			$ 4.559	$ 4.559
Proceed from issuance of convertible preferred stock | $			$ 21,000	$ 21,000	$ 21,000

Significant Accounting Polici_4

Significant Accounting Policies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018USD ($)Segment
Accounting Policies [Abstract]
Number of operating segment | Segment	1
Marketable securities with maturity of greater than one year	$ 0
Financial instruments with off-balance sheet risk of loss	$ 0

Significant Accounting Polici_5

Significant Accounting Policies - Schedule of Marketable Securities (Detail) $ in Thousands	Sep. 30, 2018USD ($)
Marketable Securities [Line Items]
Amortized Cost	$ 58,671
gross Unrealized Gains
Gross Unrealized Losses	(7)
Fair Value	58,664
Commercial Paper [Member]
Marketable Securities [Line Items]
Amortized Cost	34,569
gross Unrealized Gains
Gross Unrealized Losses	(1)
Fair Value	34,568
U. S Treasury Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	12,702
gross Unrealized Gains
Gross Unrealized Losses	(1)
Fair Value	12,701
Asset Backed Securities [Member]
Marketable Securities [Line Items]
Amortized Cost	11,400
gross Unrealized Gains
Gross Unrealized Losses	(5)
Fair Value	$ 11,395

Significant Accounting Polici_6

Significant Accounting Policies - Schedule of Fair Value of Marketable Securities (Detail) $ in Thousands	Sep. 30, 2018USD ($)
Marketable Securities [Line Items]
Marketable securities	$ 58,664
Level 1 [Member]
Marketable Securities [Line Items]
Marketable securities	12,701
Level 2 [Member]
Marketable Securities [Line Items]
Marketable securities	45,963
Commercial Paper [Member]
Marketable Securities [Line Items]
Marketable securities	34,568
Commercial Paper [Member] | Level 2 [Member]
Marketable Securities [Line Items]
Marketable securities	34,568
U. S Treasury Securities [Member]
Marketable Securities [Line Items]
Marketable securities	12,701
U. S Treasury Securities [Member] | Level 1 [Member]
Marketable Securities [Line Items]
Marketable securities	12,701
Asset Backed Securities [Member]
Marketable Securities [Line Items]
Marketable securities	11,395
Asset Backed Securities [Member] | Level 2 [Member]
Marketable Securities [Line Items]
Marketable securities	$ 11,395

Significant Accounting Polici_7

Significant Accounting Policies - Schedule of Potential Shares Outstanding Excluded in Computation of Diluted Net Loss Per Common Share (Detail) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Shares issuable upon conversion of Series A Preferred [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities that could potentially dilute basic earnings per share		12,428,773
Shares issuable upon exercise of stock options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities that could potentially dilute basic earnings per share	1,507,268	90,429
Non-vested shares under restricted stock grants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities that could potentially dilute basic earnings per share	848,859	848,859

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - PBM Capital Group, LLC [Member] - USD ($)	Dec. 02, 2015	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Services agreement initial term	12 months	12 months
Expenses incurred under services agreement		$ 150,000	$ 7,500	$ 307,500	$ 22,500
Due to related party		38,000		$ 38,000		$ 14,000
Service Agreement [Member]
Related Party Transaction [Line Items]
Monthly management fee payable	$ 2,500
Amended Service Agreement [Member]
Related Party Transaction [Line Items]
Monthly management fee payable		$ 50,000

Accrued Expenses - Accrued Expe

Accrued Expenses - Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued Liabilities Current [Abstract]
Compensation and related costs	$ 855	$ 49
Clinical trials and drug development	83	233
Consulting - former Chief Scientific Officer	282	0
Professional fees	26	129
Other	100	38
Total accrued expenses	$ 1,346	$ 449

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)claim$ / h	Dec. 31, 2017USD ($)claim	Mar. 22, 2018USD ($)
Loss Contingencies [Line Items]
Number of litigation against the company | claim	0	0
Accrued expenses	$ 1,346,000	$ 449,000
Former Chief Executive Officer [Member]
Loss Contingencies [Line Items]
Consulting agreement required cash payment per month	$ 29,375
Consulting payment per hour | $ / h	300
Accrued expenses	$ 300,000
Crude Cantharidin Material [Member]
Loss Contingencies [Line Items]
Purchase Commitment	$ 500,000		$ 2,300,000
Purchase agreement term	5 years

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands	Jun. 19, 2018USD ($)$ / sharesshares	Mar. 07, 2018USD ($)$ / sharesshares	Feb. 20, 2018USD ($)$ / sharesshares	Dec. 15, 2017USD ($)$ / sharesshares	Dec. 02, 2015USD ($)Investorshares	Sep. 30, 2018USD ($)$ / sharesshares	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)
Stockholders Equity [Line Items]
Common stock, authorized | shares	200,000,000					200,000,000		33,236,900
Common stock, par value | $ / shares	$ 0.0001					$ 0.0001		$ 0.0001
Common stock, voting right						1
Proceeds from initial public offering						$ 86,250
Repurchase of stocks | shares						105,144		105,144
Preferred stock shares issued | shares						0		0
Series A Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred stock shares issued | shares					21,302,972
Proceeds from issuance of convertible preferred stock					$ 1,900
Conversion of notes payable and accrued interest					500
Preferred stock subscription receivable					8,500
Stock issuance cost					$ 400		$ 95
Proceeds from stock subscription receivable								$ 8,000
Number of investors | Investor					14
Gross proceed							$ 2,700
Series A Convertible Preferred Stock [Member] | PBMVP Holdings [Member]
Stockholders Equity [Line Items]
Proceeds from stock subscription receivable									$ 500
Series B Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Common stock issued and sale | shares				1,937,984
Issuance price | $ / shares				$ 2.58
Gross proceed				$ 5,000
Series C Convertible Preferred Stock [Member]
Stockholders Equity [Line Items]
Common stock issued and sale | shares		4,606,267	4,606,267
Stock issuance cost						$ 7
Issuance price | $ / shares		$ 4.559	$ 4.559
Gross proceed		$ 21,000	$ 21,000			$ 21,000
Amended and Restated Agreement [Member]
Stockholders Equity [Line Items]
Repurchase of stocks | shares						848,859
Repurchase price | $ / shares						$ 0.0001
IPO [Member]
Stockholders Equity [Line Items]
Common stock issued and sale | shares	5,750,000					2,198,198
Offering price | $ / shares	$ 15
Proceeds from initial public offering	$ 78,400
Stock issuance cost						$ 7,876
Conversion of preferred stock into common stock, shares | shares	16,246,872
IPO [Member] | Series A Preferred Stock [Member]
Stockholders Equity [Line Items]
Conversion of preferred stock into common stock, shares | shares	12,428,773
IPO [Member] | Series B Preferred Stock [Member]
Stockholders Equity [Line Items]
Conversion of preferred stock into common stock, shares | shares	1,130,679
IPO [Member] | Series C Preferred Stock [Member]
Stockholders Equity [Line Items]
Conversion of preferred stock into common stock, shares | shares	2,687,420

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Jun. 19, 2018	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation		$ 0.3			$ 0.3
Employee Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted contractual term					10 years
Stock option vesting term, description					Through 2,022
Stock options expiration term, description					Through 2,028
Expected dividend yield		0.00%	0.00%	[1]	0.00%	0.00%
Share based compensation arrangement by share based payment award stock option, shares granted			0		1,416,839
Weighted average grant date fair value per share					$ 6.91	$ 0.12
Employee Stock Options [Member] | Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of stock subject to vesting (as a percent)					25.00%
Stock vesting period					12 months
Employee Stock Options [Member] | Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of stock subject to vesting (as a percent)					75.00%
Stock vesting period					12 months
Non-Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield		0.00%	0.00%		0.00%	0.00%
Share based compensation arrangement by share based payment award stock option, shares granted		0	0		0	0
Employee And Non Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation		$ 7			$ 7
Weighted-average stock option recognize period					1 year 6 months
IPO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for issuance		3,738,199			3,738,199
Shares issued	5,750,000				2,198,198
Number of years reserved share increase					10 years
Annual Increase in number of common shares from January 1, 2019 through January 1, 2028					4.00%
Shares available for grant		1,989,033			1,989,033
[1]	The Company did not grant stock options during the three months ended September 30, 2017

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions Used to Estimate Fair Value Employee Stock Options (Detail) - Employee Stock Options [Member] - $ / shares	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	[1]	Sep. 30, 2018	Sep. 30, 2017
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Exercise price				$ 8.31	$ 0.90
Risk-free rate of interest, minimum	2.80%			2.58%	1.92%
Risk-free rate of interest, maximum	3.03%			3.03%	2.23%
Expected term (years)	6 years 2 months 8 days			6 years 1 month 16 days	6 years 3 months
Expected stock price volatility, minimum	79.31%			70.58%	79.02%
Expected stock price volatility, maximum	83.18%			83.67%	79.12%
Weighted average estimated fair value share price	$ 10.90			$ 6.91	$ 0.12
Dividend yield	0.00%	0.00%		0.00%	0.00%
Minimum [Member]
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Exercise price	$ 14.36			$ 6.52
Maximum [Member]
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Exercise price	$ 16.32			$ 16.32
[1]	The Company did not grant stock options during the three months ended September 30, 2017

Stock-Based Compensation - As_2

Stock-Based Compensation - Assumptions Used to Estimate Fair Value of Employee Stock Option Awards (Parenthetical) (Detail) - shares	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018
Employee Stock Options [Member]
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Share based compensation arrangement by share based payment award stock option, shares granted	0	1,416,839

Stock-Based Compensation - As_3

Stock-Based Compensation - Assumptions Used to Estimate Fair Value of Non-employee Stock Options (Detail) - Non-Employee Stock Option [Member] - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Exercise price	$ 0.90	$ 0.90	$ 0.90	$ 0.90	$ 0.90
Risk-free rate of interest, minimum	2.81%	2.16%	2.33%	2.16%
Risk-free rate of interest, maximum	3.01%	2.33%	3.01%	2.48%
Expected term (years)	7 years 6 months 14 days	8 years 6 months 14 days	7 years 8 months 1 day	8 years 7 months 9 days
Expected stock price volatility, minimum	79.34%	77.92%	68.98%	77.92%
Expected stock price volatility, maximum	83.81%	78.84%	83.81%	79.12%
Weighted average share price	$ 15.78	$ 0.15	$ 13.92	$ 0.15
Dividend yield	0.00%	0.00%	0.00%	0.00%

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Employee Stock Option Activity (Detail) - Employee Stock Options [Member] - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, Outstanding Beginning Balance		17,502
Number of shares, Options granted	0	1,416,839
Number of shares, Outstanding Ending Balance		1,434,341
Number of shares, Options vested and exercisable Ending Balance		7,294
Weighted average exercise price, Outstanding Beginning Balance		$ 0.90
Weighted average exercise price, Options granted		8.31	$ 0.90
Weighted average exercise price, Outstanding Ending Balance		8.22
Weighted average exercise price, Options vested and exercisable Ending Balance		$ 0.90
Weighted average remaining contractual life (in years), Outstanding		9 years 4 months 24 days
Weighted average remaining contractual life (in years), Options vested and exercisable		8 years 3 months 18 days
Aggregate intrinsic value, Outstanding Ending Balance		$ 11,517,050
Aggregate intrinsic value, Options vested and exercisable Ending Balance		$ 111,963

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Company's Non-Employee Stock Option Activity (Detail) - Non-Employee Stock Option [Member] - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, Outstanding Beginning Balance			72,927
Number of shares, Options granted	0	0	0	0
Number of shares, Outstanding Ending Balance	72,927		72,927
Number of shares, Options vested and exercisable Ending Balance	52,265		52,265
Weighted average exercise price, Outstanding Beginning Balance			$ 0.90
Weighted average exercise price, Options granted			0
Weighted average exercise price, Outstanding Ending Balance	$ 0.90	$ 0.90	0.90	$ 0.90
Weighted average exercise price, Options vested and exercisable Ending Balance	$ 0.90		$ 0.90
Weighted average remaining contractual life (in years), Outstanding			7 years 6 months
Weighted average remaining contractual life (in years), Options vested and exercisable			7 years 6 months
Aggregate intrinsic value, Outstanding Ending Balance	$ 1,119,429		$ 1,119,429
Aggregate intrinsic value, Options vested and exercisable Ending Balance	$ 802,268		$ 802,268

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Restricted Stock Awards Activites (Detail) - Restricted Stock [Member]	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, Weighted Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 0.33
Nonvested, Weighted Average Grant Date Fair Value, Granted | $ / shares	0
Nonvested, Weighted Average Grant Date Fair Value, Ending Balance | $ / shares	$ 0.33
Nonvested, Number of Shares, Beginning Balance | shares	848,859
Nonvested, Number of Shares, Granted | shares	0
Nonvested, Number of Shares, Ending Balance | shares	848,859

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 1,516	$ 3,099	$ 3
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	40	507	$ 3
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 1,476	$ 2,592