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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Trading Symbol	KRYS
Entity Registrant Name	Krystal Biotech, Inc.
Entity Central Index Key	0001711279
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		10,237,247

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets
Cash	$ 52,570	$ 1,923
Prepaid research and development expenses	48	246
Total current assets	52,618	2,169
Property and equipment, net	55	13
Total assets	52,673	2,182
Current liabilities
Accounts payable	550	42
Accrued expenses and other current liabilities	1,925	1
Total current liabilities	2,475	43
Accrued interest		7
Related party convertible promissory notes	0	698
Convertible promissory notes		1,145
Total liabilities	2,475	1,893
Commitments and contingencies (Note 7)
Convertible preferred stock
Convertible preferred stock	0	0
Convertible preferred stock	0	0
Stockholders' and members' equity (deficit)
Common stock; $0.00001 par value; 80,000,000 shares authorized, 10,237,247 shares issued and outstanding at September 30, 2017 (unaudited); no shares authorized, issued, or outstanding at December 31, 2016	0	0
Common units; no common units authorized, issued, or outstanding at September 30, 2017 (unaudited); no par value; 3,490,884 units authorized, issued, and outstanding at December 31, 2016	0	0
Preferred units; no par value; no preferred units authorized, issued, or outstanding at September 30, 2017 (unaudited); no par value; 179,613 units authorized, issued, and outstanding at December 31, 2016 (aggregate liquidation preference of $1,406)	0	1,406
Additional paid-in capital	57,875	33
Accumulated deficit	(7,677)	(1,150)
Total stockholders' and members' equity	50,198	289
Total liabilities, convertible preferred stock and stockholders' and members' equity	$ 52,673	$ 2,182

Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.00001	$ 0.00001
Convertible preferred stock, shares authorized	20,000,000	0
Convertible preferred stock, shares issued	2,061,773	0
Convertible preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	80,000,000	0
Common stock, shares issued	10,237,247	0
Common stock, shares outstanding	10,237,247	0
Common units, no par value
Common units, shares authorized	0	3,490,884
Common units, shares issued	0	3,490,884
Common units, shares outstanding	0	3,490,884
Preferred units, no par value
Preferred units, shares authorized	0	179,613
Preferred units, shares issued	0	179,613
Preferred units, shares outstanding	0	179,613
Preferred units, aggregate liquidation preference		$ 1,406

Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Condensed Statements of Operations - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Expenses
Research and development	$ 1,355	$ 241	$ 2,120	$ 339
General and administrative	738	81	1,154	184
Total operating expenses	2,093	322	3,274	523
Loss from operations	(2,093)	(322)	(3,274)	(523)
Other Expense
Interest expense, net	(3,180)		(3,253)
Total other expense	(3,180)		(3,253)
Net loss	(5,273)	(322)	(6,527)	(523)
Net loss applicable to stockholders and members	$ (5,273)	$ (322)	$ (6,527)	$ (523)
Net loss attributable to common stockholders per share:
Basic and diluted	$ (1.26)	$ (8.48)	$ (1.75)	$ (40.20)
Weighted-average common shares and common units outstanding
Basic and diluted	4,183,075	37,982	3,725,825	13,016

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
Condensed Statements of Cash Flows - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Operating Activities
Net loss	$ (6,527)	$ (523)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	9	1
Stock-based compensation expense	188	7
Non-cash interest expense	3,263
(Increase) decrease in
Prepaid research and development expenses	198	(12)
Increase (decrease) in
Accounts payable	271	62
Accrued expenses and other current liabilities	835	15
Net cash used in operating activities	(1,763)	(450)
Investing Activities
Purchases of property and equipment	(51)	(6)
Net cash used in investing activities	(51)	(6)
Financing Activities
Proceeds from the issuance of convertible promissory notes	2,299
Issuance of common stock and common units, net	43,162	100
Issuance of preferred stock and preferred units	7,000	754
Net cash provided by financing activities	52,461	854
Net increase in cash	50,647	398
Cash at beginning of period	1,923
Cash at end of period	52,570	398
Supplemental Disclosures of Non-Cash Investing and Financing Activities
Conversion of common units to preferred units		$ 100
Conversion of convertible promissory notes to preferred stock	4,142
Conversion of preferred stock to common stock	12,661
Unpaid deferred offering costs	$ 1,327

Organization

9 Months Ended

Sep. 30, 2017

Accounting Policies [Abstract]

Organization

1.	Organization

Krystal Biotech, Inc. (the “Company,” or “we” or other similar pronouns) was formed on December 20, 2015 in the State of California as Krystal Biotech, LLC and began operations on April 15, 2016. On March 31, 2017, the Company converted from a limited liability company (“LLC”) to a C-corporation in the state of Delaware, and changed its name to Krystal Biotech, Inc.

Stock Split and Increase in Authorized Shares

On September 5, 2017, in connection with our initial public offering (the “IPO”), the Company’s board of directors (the “Board”) approved a 1-to-4.5 forward stock split, in the form of a dividend, of all outstanding shares of common stock and preferred stock. Except as otherwise noted, all references to share and per share amounts related to common stock, common units, preferred stock, preferred units and stock options in these condensed financial statements reflect the stock split. The par value per share of our capital stock was not adjusted as a result of the stock split. Additionally, the Board approved an increase in authorized shares of common stock and preferred stock to 80,000,000 shares and 20,000,000 shares, respectively. The stock split and the increase in the number of authorized common and preferred shares occurred immediately prior to the effectiveness of our registration statement on Form S-1 (File No. 333-220085) relating to the IPO on September 19, 2017.

Initial Public Offering

On September 22, 2017, the Company completed its initial public offering of 4,554,000 shares of its common stock at a price to the public of $10.00 per share, which includes the sale of 594,000 shares of the Company’s common stock pursuant to the underwriters’ full exercise of their option to purchase additional shares. The total proceeds from the offering to the Company, net of underwriting discounts and commissions of approximately $3.2 million, were approximately $42.3 million. After deducting offering expenses payable by the Company of approximately $1.5 million, net proceeds to the Company were approximately $40.8 million. Immediately prior to the closing of the IPO, all outstanding shares of the Company’s preferred stock converted into 2,061,773 shares of common stock on a 1-to-1 basis.

Liquidity and Risks

As of September 30, 2017 and December 31, 2016, the Company had accumulated deficits since inception of $7.7 million and $1.2 million, respectively. With the net proceeds raised upon the close of IPO, the Company believes that its cash of approximately $52.6 million as of September 30, 2017 will be sufficient to allow the Company to fund its operations for at least 12 months from the filing date of this Form 10-Q. As the Company continues to incur losses, a transition to profitability is dependent upon the successful development, approval and commercialization of its product candidates and the achievement of a level of revenues adequate to support the Company’s cost structure. The Company may never achieve profitability, and unless and until it does, the Company will continue to need to raise additional capital or obtain financing from other sources, such as partnerships. Management intends to fund future operations through the sale of equity and debt financings and may also seek additional capital through arrangements with strategic partners or other sources. There can be no assurances, however, that additional funding will be available on terms acceptable to the Company, or at all.

The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, development of technological innovations by its competitors, risks of failure of clinical studies, dependence on key personnel, protection of proprietary technology, compliance with government regulations, and ability to transition from preclinical manufacturing to commercial production of products.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

Basis of Presentation

The accompanying condensed financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Unaudited Condensed Financial Information

The accompanying condensed balance sheet as of September 30, 2017, the condensed statements of operations for the three and nine months ended September 30, 2017 and 2016, and condensed statements of cash flows for the nine months ended September 30, 2017 and 2016, and the related information contained within the notes to the condensed financial statements are unaudited. As permitted under GAAP for interim financial information under instructions to Form 10-Q and Article 10 of Regulation S-X., certain footnotes or other financial information can be condensed or omitted. These financial statements and related disclosures have been prepared with the assumption that users of the interim financial information have read or have access to the audited financial statements for the preceding fiscal year. Accordingly, these statements should be read in conjunction with the audited consolidated financial statements and related notes included in our registration statement on Form S-1 relating to the IPO on September 19, 2017. The condensed financial statements have been prepared on the same basis as the annual audited financial statements and, in the opinion of management, reflect all adjustments, consisting of normal and recurring adjustments, necessary for the fair presentation of the Company’s financial position at September 30, 2017, the statements of operations for the three and nine months ended September 30, 2017 and 2016, and its cash flows for the nine months ended September 30, 2017 and 2016. The results for the three and nine months ended September 30, 2017 are not necessarily indicative of results to be expected for the year ending December 31, 2017 or any other condensed or future period.

Use of Estimates

The preparation of condensed financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the condensed financial statements and accompanying notes. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these condensed financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the condensed financial statements. Estimates are used in the following areas, among others: stock-based compensation expense, accrued research and development expenses, the fair value of financial instruments, and the valuation allowance included in the deferred income taxes calculations.

Segment and Geographical Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company and the Company’s chief operating decision maker view the Company’s operations and manage its business in one operating segment, which is the business of developing and commercializing pharmaceuticals. The Company operates in only one geographic segment.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Financial instruments that potentially subject the Company to credit risk consist of cash. The Company’s policy is to invest its cash in money market funds and various bank deposit accounts. These financial instruments were held in Company accounts at two financial institutions. The counterparties to the agreements relating to the Company’s investments consist of financial institutions of high credit standing. The Company is exposed to credit risk in the event of default by the financial institutions to the extent of amounts recorded on the balance sheets which may be in excess of insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss.

Cash

Cash consists of money market funds and bank deposit.

Deferred Issuance Costs

Deferred public offering costs, which consist primarily of direct, incremental legal and accounting fees relating to the IPO, are capitalized within other assets at December 31, 2016 and are offset against IPO proceeds at September 30, 2017.

Fair Value of Financial Instruments

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic 820, Fair Value Measurement and Disclosures, established a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the financial instrument based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the financial instrument and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported or disclosed fair value of the financial instruments and is not a measure of the investment credit quality. Fair value measurements are classified and disclosed in one of the following three categories:

•

Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

•

Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly.

•

Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

There have been no changes to the valuation methods utilized by the Company during the nine months ended September 30, 2017 and the year ended December 31, 2016. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of financial instruments between levels during the nine months ended September 30, 2017 and the year ended December 31, 2016.

The carrying amounts of financial instruments consisting of cash, prepaid expenses, accounts payable and accrued expenses, related party convertible promissory notes and convertible promissory notes included in the Company’s Condensed financial statements are reasonable estimates of fair value due to their short maturities.

Property and Equipment, net

Property and equipment is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred, while costs of major additions and betterments are capitalized. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows:


Computer equipment and software			3 years
Lab equipment			3 years

Impairment of Long-Lived Assets

The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value. The Company has not recognized any impairment losses through September 30, 2017.

Convertible Preferred Stock

In accordance with the guidance in FASB ASC Topic 480, Distinguishing Liabilities from Equity, shares of preferred stock (Note 7), were classified outside of permanent equity and within temporary equity, as of December 30, 2016 due to their associated redemption features and liquidation preferences. There were no shares of preferred stock outstanding as of September 30, 2017 and December 30, 2016.

The Company evaluated its preferred stock and determined that it is considered an equity host under ASC 815. In making this determination, the Company’s analysis followed the whole instrument approach which compares an individual feature against the entire preferred stock instrument which includes that feature. The Company’s analysis was based on a consideration of the economic characteristics and risks of the preferred stock. More specifically, the Company evaluated all of the stated and implied substantive terms and features, including: (i) whether the preferred stock included redemption features; (ii) how and when any redemption features could be exercised; (iii) whether the holders of the preferred stock were entitled to dividends and how those dividends were calculated; (iv) the voting rights of the Preferred stock; and (v) the existence and nature of any conversion rights. As a result of the Company’s conclusion that the preferred stock both represent an equity host, the redemption features of the preferred stock are considered to be clearly and closely related to the associated equity host instruments. Accordingly, the redemption features of the preferred stock are not considered embedded derivatives that require bifurcation. The Company also concluded that the conversion rights under the preferred stock are clearly and closely related to the equity host instruments and are not considered embedded derivatives that require bifurcation.

Research and Development Expenses

Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, facilities and overhead, preclinical activities and related clinical manufacturing costs, regulatory and other related costs.

The Company estimates contract research and clinical trials materials manufacturing expenses based on the services performed pursuant to contracts with research and manufacturing organizations that manufacture materials used in the Company’s ongoing preclinical studies. Nonrefundable advanced 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 delivered or the services are performed.

In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. These estimates are based on communications with the third party service providers and the Company’s estimates of accrued expenses using information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual accordingly.

Stock-Based Compensation Expense

The Company accounts for its stock-based compensation awards to employees and directors in accordance with FASB ASC Topic 718, Compensation-Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock, to be recognized in the statements of operations based on their grant date fair values. Compensation expense related to awards to employees is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Share-based payments issued to non-employees are recorded at their fair values, and are periodically revalued as the equity instruments vest and are recognized as expense over the related service period in accordance with the provisions of ASC 718 and ASC Topic 505, Equity, and are expensed using an accelerated attribution model. The Company estimates the fair value of its stock options using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including: (i) the expected stock price volatility; (ii) the expected term of the award; (iii) the risk-free interest rate; (iv) expected dividends; and (v) the estimated fair value of its common stock on the measurement date. Due to the lack of a public market for the trading of its Common Stock and a lack of Company-specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected term of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Due to the lack of Company-specific historical option activity, the Company has estimated the expected term of its employee stock options using the “simplified” method, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option. The expected term for non-employee awards is the remaining contractual term of the option. The risk-free interest rates are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid, and does not expect to pay dividends in the foreseeable future. The Company is also required to estimate forfeitures at the time of grant, and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate forfeitures and records stock-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company’s estimates, the differences are recorded as a cumulative adjustment in the period the estimates were revised. Stock-based compensation expense recognized in the Condensed financial statements is based on awards that are ultimately expected to vest.

Net Loss Per Share Attributable to Common Stockholders and Members

On March 31, 2017, the Company converted from an LLC to a C-corporation. Upon the conversion, each outstanding common unit and preferred unit (Note 7) were converted into one share of common stock and preferred stock, respectively. Common units had similar rights and characteristics of common stock issued upon the conversion. In calculating net loss per share, the Company retrospectively applied the effects of the conversion to the number of common units outstanding prior to the conversion. Net loss per share for periods prior to the conversion to a C-corporation refers to net loss per common unit.

Basic net loss per share attributable to common stockholders is calculated by dividing net loss attributable to common stockholders by the weighted average shares outstanding during the period, without consideration for common stock equivalents. During periods of income, the Company allocates participating securities a proportional share of income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities (the “two-class method”). The Company’s convertible preferred stock participate in any dividends declared by the Company and are therefore considered to be participating securities. Participating securities have the effect of diluting both basic and diluted earnings per share during periods of income. During periods of loss, the Company allocates no loss to participating securities because they have no contractual obligation to share in the losses of the Company. Diluted net loss per share attributable to common stockholders is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock and if-converted methods. For purposes of the diluted net loss per share and per unit attributable to common stockholders calculation, preferred stock, and stock options are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share and per unit were the same for all periods presented.

Comprehensive Loss

Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources. The Company is required to record all components of comprehensive loss in the Condensed financial statements in the period in which they are recognized. Net loss and other comprehensive loss are reported, net of their related tax effect, to arrive at a comprehensive loss. For the three and nine months ended September 30, 2017 and 2016, comprehensive loss was equal to the net loss.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02 Leases (Topic 842) (“ASU 2016-02”), which replaces the existing lease accounting standards. The new standard requires a dual approach for lessee accounting under which a lessee would account for leases as finance (also referred to as capital) leases or operating leases. Both finance leases and operating leases will result in the lessee recognizing a right-of-use asset and corresponding lease liability. For finance leases the lessee would recognize interest expense and amortization of the right-of-use asset and for operating leases the lessee would recognize straight-line total lease expense. ASU 2016-02 is effective for fiscal years, and condensed periods within those years, beginning after December 15, 2018. The Company generally does not finance purchases of equipment but it does lease office and lab facilities. The Company is in the process of evaluating the effect that this ASU will have on its condensed financial statements and related disclosures.

Property and Equipment, Net

9 Months Ended

Sep. 30, 2017

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

3.	Property and Equipment, Net

Property and equipment, net consist of the following (in thousands):


	September 30, 2017			December 31, 2016
	(unaudited)
Computer equipment and software	$	9		$	8
Laboratory equipment		57			7

Total property and equipment		66			15
Accumulated depreciation and amortization		(11	)		(2	)

Property and equipment, net	$	55			13

Depreciation expense was $5 thousand and $9 thousand for the three and nine months ended September 30, 2017, respectively, and $0 and $1 thousand for the three and nine months ended September 30, 2016, respectively.

Convertible Promissory Notes

9 Months Ended

Sep. 30, 2017

Debt Disclosure [Abstract]

Convertible Promissory Notes

4.	Convertible Promissory Notes

General

On November 16, 2016, the Company entered into a Note Purchase Agreement (the “Note Purchase Agreement”) for the issuance of convertible promissory notes (the “Notes”) due May 2018. The Notes bore interest at a rate of 6% per annum, which accrued based on a 365-day year. The Notes would have become immediately due and payable in the event of an occurrence of default by the Company. In accordance with their terms, as amended in July 2017, the principal and accrued interest under the Notes were converted into an aggregate of 968,053 shares of preferred stock upon the closing of the Sun Pharma Offering (as defined in Note 7) on August 8, 2017. These shares of preferred stock were then converted into shares of common stock on a 1-to-1 basis upon closing of the IPO.

Conversion Features

The terms of the Notes provided that, in the event the Company sells, merges, consolidates or reorganizes, where the equity owners of the Company own less than 50% of the voting shares post acquisition, then all the outstanding Notes, at the option of the Note holders, either: (i) become immediately due and payable, or (ii) convert into a number of shares of common stock or common units (rounded down to the nearest share), obtained by dividing the outstanding Notes converted by dividing the target valuation of $16.0 million by the fully diluted shares.

Furthermore, in the event that the Company shall issue and sell preferred units in the Company , or if the Company has converted into a corporation, shares of the preferred stock of the Company (in either case, the “Preferred Securities”), to investors for aggregate proceeds to the Company of not less than $5.0 million, then the Notes shall be automatically converted into a number of shares of Preferred Securities equal to the quotient arrived at by dividing the balance of the outstanding Notes so converted by a price per unit or share that is the lesser of: (i) 80% of the per unit or share price of the Preferred Securities issued upon the conversion; or (ii) the target valuation of $16.0 million divided by the fully diluted units or shares immediately prior to closing of the offering which triggered the conversion.

In July 2017, the Notes were amended so that they would also automatically convert upon the closing of an IPO into shares of common stock.

As of September 30, 2017 and December 31, 2016, the Company had outstanding balances related to the Notes of $0 and $1.8 million, respectively. Additionally, as of September 30, 2017 and December 31, 2016, the Company had accrued interest related to the Notes of $0 and $7 thousand, respectively.

Interest expense related to the Notes was $32 thousand and $106 thousand for the three and nine months ended September 30, 2017, respectively, and $0 for each of the three and nine months ended September 30, 2016.

On August 8, 2017, the Notes plus accrued interest were converted into 968,053 shares of preferred stock upon the closing of the Sun Pharma Offering.

On September 22, 2017, all outstanding shares of preferred stock converted into shares of common stock on a 1-to-1 basis upon the closing of the Company’s IPO.

Related Party Convertible Promissory Notes

9 Months Ended

Sep. 30, 2017

Accounting Changes and Error Corrections [Abstract]

5	Related Party Convertible Promissory Notes

On November 14, 2016, the Company issued a convertible promissory note, in the amount of $250 thousand, under the Note Purchase Agreement (Note 4) to a party related to a director of the Company. The terms of the Notes issued to the related party were at an arm’s-length and identical to the Notes discussed in Note 4.

On December 27, 2016, the Company issued a convertible promissory note, in the amount of $448 thousand, under the Note Purchase Agreement (Note 4) to an affiliate of two executive officers and directors of the Company. The terms of the Notes issued to the related party were at an arm’s-length and identical to the Notes discussed in Note 4.

On May 17, 2017, the Company issued a convertible promissory note, in the amount of $250 thousand, under the Note Purchase Agreement (Note 4) to an affiliate of a director of the Company. The terms of the Notes issued to the related party were at an arm’s-length and identical to the Notes issued and discussed in Note 4.

On June 6, 2017, the Company executed a second Note Purchase Agreement (the “Second Note Purchase Agreement”) for the issuance of a convertible promissory note to a director of the Company (the “June Note”) in the amount of $750 thousand due May 2018. The June Note bore interest at a rate of 6% per annum, which is accrued based on a 365 day year. The June Note would have become immediately due and payable in the event of an occurrence of default by the Company.

Conversion Features

The June Note is convertible into shares of preferred stock automatically upon our closing of a preferred stock financing of at least $5.0 million, or into shares of common stock upon the closing of an initial public offering. The conversion price of the June Note is 80% of the sales price of the preferred stock or 80% of the price at which our common stock is offered to the public in an initial public offering.

As of September 30, 2017 and December 31, 2016, accrued interest on related party convertible promissory notes was $0 and $2 thousand, respectively.

Interest expense related to the related party convertible promissory notes was $12 thousand and $37 thousand for the three and nine months ended September 30, 2017, respectively, and $0 for each of the three and nine months ended September 30, 2016.

On August 8, 2017, upon the closing of the Sun Pharma Offering, the Notes and the June Note plus accrued interest thereon, consisting of $40 thousand, were converted into 360,311 shares of preferred stock. On September 22, 2017, all outstanding shares of preferred stock converted into 2,061,773 shares of common stock on a 1-to-1 basis upon the closing of the IPO.

Commitments and Contingencies

9 Months Ended

Sep. 30, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

6	Commitments and Contingencies

Significant Contracts and Agreements

Lease Agreement

In May 2016, the Company signed an operating lease for laboratory and office space that commenced in June 2016 and expired on October 31, 2017 (the “2016 Lease”). In June 2016, the Company entered into an amendment to the 2016 Lease (the “First Amendment to the 2016 Lease”), which amended the timing of the rent payment from one single payment to 17 equal monthly installments. On February 27, 2017, the Company entered into a second amendment to the 2016 Lease, which extended the expiration date of the 2016 Lease to October 31, 2018.

As of September 30, 2017, future minimum operating lease payments and future minimum payments to be received from non-cancelable subleases were as follows (in thousands):


	Operating Leases
2017 (remaining three months)	$	28
2018		103
2019		—
2020		—
2021		—
Thereafter		—

Future minimum operating lease payments		131
Less: minimum payments to be received from non-cancelable subleases		(23	)

Total minimum lease payments, net	$	108

The Company recorded $20 thousand and $59 thousand in rent expense for the three and nine months ended September 30, 2017, respectively, and recorded $24 thousand and $35 thousand in rent expense for the three and nine months ended September 30, 2016, respectively.

Capitalization

9 Months Ended

Sep. 30, 2017

Equity [Abstract]

Capitalization

7.	Capitalization

Conversion to C-Corporation

On March 31, 2017, the Company converted from an LLC to a C-Corporation. Upon the conversion, all outstanding preferred units and common units were converted on a 1-to-1 basis into shares of preferred stock and common stock, respectively. Following the conversion, the Company had 450,000 authorized shares of preferred stock, $0.00001 par value per share, of which 179,613 shares were issued and outstanding and 45,000,000 authorized shares of common stock, par value $0.00001 per share, of which 3,490,884 shares were issued and outstanding.

Initial Public Offering

Shares Outstanding

As of September 30, 2017, 10,237,247 shares of common stock were outstanding. As of September 30, 2017, no shares of preferred stock were outstanding.

As of December 31, 2016, 3,490,884 common units and 179,613 preferred units were outstanding.

Issuance of Preferred Stock and Conversion of Convertible Promissory Notes and Related Party Convertible Promissory Notes

On August 4, 2017, the Company amended its articles of incorporation to authorize 1,500,000 shares of common stock, par value $0.00001 per share, and 1,500,000 shares of preferred stock, par value $0.00001 per share, of which 179,613 shares were designated as Series Seed preferred stock (the “Series Seed Preferred Stock”), 210,000 shares were designated as Series A preferred stock (the “Series A Preferred Stock”), 200,000 shares were designated as Series A-1 preferred stock (the “Series A-1 Preferred Stock”) and 30,000 shares were designated as Series A-2 preferred stock (the “Series A-2 Preferred Stock”). The Series Seed Preferred Stock, Series A-1 Preferred Stock and Series A-2 Preferred Stock are collectively known as the preferred stock.

On August 8, 2017, the Company issued 914,107 shares of Series A Preferred Stock to a single investor (“Sun Pharma”) at a purchase price of $7.66 per share for aggregate proceeds of approximately $7.0 million (the “Sun Pharma Offering”). Concurrently with the issuance of the Series A Preferred Stock, and in accordance with the conversion features of the Notes (Note 4), all outstanding Notes plus accrued interest thereon were automatically converted into shares of preferred stock.

The following table outlines the conversion on August 8, 2017 of the Notes into shares of preferred stock (in thousands except share and per share amounts):


	Principal		Accrued Interest		Total		Conversion Price Per Share⁽¹⁾			Shares of Series A-1		Shares of Series A-2		Fair Value Date of Conversion		Fair Value Series A-1		Fair Value Series A-2		Loss on Extinguishment of Convertible Promissory Notes
Convertible promissory notes	$	2,444	$	72	$	2,516	$	4.14	⁽¹⁾		607,743		—	$	7.66	$	4,654	$	—	$	(2,138	)

Related party convertible promissory notes		948		32		980	$	4.14	⁽¹⁾		236,619		—	$	7.66		1,812		—		(832	)
Related party convertible promissory notes—June Note		750		8		758	$	6.13	⁽²⁾		—		123,691	$	7.66		—		947		(189	)

Total related party promissory notes		1,698		40		1,738					236,619		123,691				1,812		947		(1,021	)

Total	$	4,142	$	112	$	4,254					844,362		123,691			$	6,466	$	947	$	(3,159	)

(1)	The conversion price was determined by dividing the target valuation of $16 million by the outstanding shares of 3,863,547 immediately prior to the issuance of the Series A on August 8, 2017 (Note 4).

(2)	The conversion price was determined to be 80% of the $7.66 sales price per share of the Series A shares issued on August 8, 2017 (Note 5).

Issuance of Common Stock

On August 25, 2017, following the completion of the Sun Pharma Offering, Daniel S. Janney, a member of our board of directors, purchased 130,590 shares of our common stock at the same price per share paid by Sun Pharma, $7.66 per share, through an investment entity owned and controlled by a board member for a total consideration of approximately $1.0 million.

Preferred Units and Preferred Stock

On April 15, 2016, the Company authorized 100 member units and issued 450 member units for aggregate proceeds of $100 thousand. On September 30, 2017, the Company converted all of the member units into 12,771 preferred units at an issue price of $7.83 (the “Original Issue Price”) per share plus 3,490,884 common units, and issued an additional 96,345 preferred units at the Original Issue Price for aggregate proceeds of $754 thousand. On December 27, 2016, the Company issued an additional 70,497 preferred units at the Original Issue Price for aggregate proceeds of $552 thousand. On March 31, 2017, all of the preferred units were converted into preferred stock on a 1-to-1 basis. As of September 22, 2017, all of the preferred stock was converted to common stock in connection with the Company’s IPO (Note 1). As of September 30, 2017 and December 31, 2016, the Company had balances of preferred units of $0 and $1.4 million, respectively.

The rights, preferences and privileges of the preferred stock consisted of the following:

Conversion. Each share of preferred stock shall be convertible at the option of the holder at any point in time into fully paid and non-assessable shares of common stock. Upon conversion, the preferred stock would be fully settled. Each share of preferred stock was convertible into that number of shares of common stock as determined by dividing the Original Issue Price of such share by the applicable conversion price. As of December 31, 2016, the conversion rate was 1-to-1, but was subject to future adjustments to the conversion price upon the occurrence of certain events including: (i) certain issuances of common stock at a price less than the conversion price in effect on the date of such issuance; and (ii) future stock splits, subdivisions, or combinations of outstanding common stock.

Each share of preferred stock shall automatically be converted into shares of common stock at the conversion price at the time in effect for such series of preferred upon the earlier of: (i) a qualified public offering, as defined in the Certificate of Incorporation; or (ii) the majority vote of the holders of preferred stock on a per share and as-converted to common stock basis.

Voting Rights. The holders of shares of preferred stock are entitled to one vote for each share of preferred stock held at all meetings of stockholders and written actions in lieu of meetings. The Board shall be elected by vote of the common stock and the preferred stock voting together as a single class on an as-converted basis.

Dividends. The holders of the preferred stock are entitled to receive dividends, if and when declared by the Board, and all dividends shall be paid pro rata on the common stock and the preferred stock, without preference, based on the number of shares of the common stock of the holders. From inception through September 30, 2017, no dividends have been declared or paid by the Company.

Liquidation Preference. In the event of any liquidation, dissolution, winding up, consolidation or merger of the Company, the holders of the preferred stock shall be entitled to receive out of the assets of the Company, prior and in preference to any distribution to the holders of common stock, an amount equal to the Original Issue Price per share, plus all declared and unpaid dividends.

The preferred units have the same rights, preferences and privileges as the preferred stock with the exception of conversion rights or liquidation preferences in the event of a merger or consolidation.

Common Units and Common Stock

On September 30, 2016, in connection with the conversion of the member units into preferred units, the Company also issued 3,490,884 common units. On March 31, 2017, in connection with the conversion of the LLC to a C-Corporation, all of the common units were converted, on a 1-to-1 basis, into shares of common stock.

The voting, dividend and liquidation rights of the holders of the common stock are subject to and qualified by the rights, powers and privileges of the holders of the preferred stock and are as follows:

Voting Rights. The holders of shares of common stock are entitled to one vote for each share of common stock held at all meetings of stockholders and written actions in lieu of meetings. The Board shall be elected by vote of the Common Stock and the Preferred stock voting together as a single class on an as-converted basis.

Dividends. The holders of the common stock are entitled to receive dividends, if and when declared by the Board , and all dividends shall be paid pro rata on the common stock and the preferred stock, without preference, based on the number of shares of the common stock of the holders. From inception through September 30, 2017, no dividends have been declared or paid by the Company.

Liquidation Preference. After payment to the holders of shares of preferred stock of their liquidation preferences, the holders of the common stock are entitled to share ratably in the Company’s assets available for distribution to stockholders, in the event of any voluntary or involuntary liquidation, dissolution, winding up, consolidation or merger of the Company or upon the occurrence of a deemed liquidation event.

Significant Agreements

9 Months Ended

Sep. 30, 2017

Commitments and Contingencies Disclosure [Abstract]

Significant Agreements

8.	Significant Agreements

Clinical Supply Agreement

In December 2016, the Company entered into a product manufacturing and clinical supply agreement with a Contract Manufacturing Organization (the “CMO”). The product manufacturing and clinical supply agreement provides the terms and conditions under which the CMO will formulate, fill, inspect, package, label and test our lead product, KB103 for clinical supply. The Company is obligated to pay the CMO for each batch of KB103 manufactured. Additionally, certain raw materials, supplies, outsourced testing and other services for the purposes of batch production will be invoiced separately by the CMO. The estimated remaining commitment under this agreement for the manufacturing of our drug product is approximately $1.7 million. The Company is also responsible for the payment of a monthly service fee for project management services for the duration of the arrangement. The Company has incurred expenses under this agreement of $483 thousand and $643 thousand for the three and nine months ended September 30, 2017, respectively, and $0 for the three and nine months ended September 30, 2016.

Stock-Based Compensation

9 Months Ended

Sep. 30, 2017

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

Stock-Based Compensation

9.	Stock-Based Compensation

On October 1, 2016, the Board of Managers adopted the 2016 Equity Incentive Plan (the “2016 Plan”), which authorizes the issuance of up to 189,472 incentive units to purchase common units.

The 2016 Plan provided for the issuance of incentive units to employees, members of the Board of Managers, and consultants of the Company. The incentive units generally expire ten years following the date of grant. The incentive units typically vest over a period of four years, but vesting provisions can vary by award based on the discretion of the Board of Managers. Incentive units to purchase common units carry an exercise price equal to the estimated fair value of the Company’s common units on the date of grant. Generally incentive units to purchase common units of the Company are exercised by payment of the exercise price in cash. Upon the termination of service, except by death or disability, of a holder of incentive units awarded under the 2016 Plan, all unvested units are forfeited and vested incentive units may be exercised within three months of termination by the holder. Common units issued as a result of awards under the 2016 Plan may be subject to repurchase provisions as designated in each individual award agreement.

On March 31, 2017, the Board adopted the 2017 Stock Incentive Plan (the “2017 Plan”) which authorized the issuance of up to 193,050 shares of the Company’s common stock under the plan. Commensurate with the opening of the 2017 Plan, all 113,683 outstanding incentive units granted under the 2016 Plan were converted into 113,683 options to purchase the Company’s common stock under the 2017 Plan. Upon the adoption of the 2017 Plan, the 2016 Plan terminated and there were no incentive units outstanding.

The 2017 Plan provided for the issuance of stock options, restricted stock awards and unrestricted stock awards to employees, members of the Board, and consultants of the Company. The Company has not granted restricted or unrestricted stock awards under the 2017 Plan since its inception. Options generally expire ten years following the date of grant. Options typically vest over a period of four years, but vesting provisions can vary by award based on the discretion of the Board. Options to purchase common stock carry an exercise price equal to the estimated fair value of the Company’s common stock on the date of grant. Generally options to purchase shares of the Company’s common stock are exercised by payment of the exercise price in cash. Upon the termination of service, except by death or disability, of a holder of stock options awarded under the 2017 Plan, all unvested options are forfeited and vested options may be exercised within three months of termination by the holder. Shares of common stock issued as a result of awards under the 2017 Plan may be subject to repurchase provisions as designated in each individual award agreement.

Shares of common stock underlying awards previously issued under the 2017 Plan which are reacquired by the Company, withheld by the Company in payment of the purchase price, exercise price, or withholding taxes; expired; cancelled due to forfeiture, or otherwise terminated other than by exercise, are added to the number of shares of common stock available for issuance under the 2017 Plan. Shares available for issuance under the 2017 Plan may be authorized but unissued shares of the Company’s common stock or common stock reacquired by the Company and held in treasury. The 2017 Plan terminated upon the adoption of the 2017 IPO Plan (as defined below).

On September 5, 2017, the Board approved the establishment of the Krystal Biotech, Inc. 2017 IPO Plan (the “2017 IPO Plan”), which was adopted prior to the effectiveness of our registration statement. Under the 2017 IPO Plan, the Company may grant incentive stock options, non-qualified stock options, stock appreciation rights, dividend equivalent rights, restricted stock, and stock grants to purchase up to 900,000 shares of the Company’s Common Stock.

The Company granted 71,649 and 142,105 stock options during the nine months ended September 30, 2017 and through December 31, 2016, respectively, to employees, consultants and board members, which are included in the following table. The options vest ratably over a four-year period, and have a life of ten years. Stock options issued to non-employees are accounted for using the fair value method of accounting, and are periodically revalued as the options vest, and are recognized as expense over the related service period.

The following table summarizes the Company’s stock option activity:


	Shares			Weighted- average Exercise Price		Weighted- average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (In thousands) ⁽¹⁾




Outstanding at January 1, 2016		—
Granted		142,105		$	2.46		9.7	$	—
Exercised		—
Cancelled or forfeited		—

Outstanding at December 31, 2016		142,105		$	2.46		9.7	$	338
Granted (unaudited)		71,649		$	6.22
Exercised (unaudited)		—			—
Cancelled or forfeited (unaudited)		(28,422	)	$	2.46

Outstanding at September 30, 2017 (unaudited)		185,332		$	3.91		9.3	$	1,122

Exercisable at September 30, 2017 (unaudited)		18,945		$	2.46		8.9	$	142

Vested at September 30, 2017 (unaudited)		18,945		$	2.46		8.9	$	142

(1)	The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at September 30, 2017 (unaudited) and December 31, 2016.

As of September 30, 2017, 900,000 shares of common stock were available for future grants under the 2017 IPO Plan.

The weighted-average grant-date fair value of options granted to employees during the nine months ended September 30, 2017 was $6.42.

Stock-based compensation expense for the three and nine months ended September 30, 2017 and 2016 relates solely to stock options granted under the 2017 Plan. The Company has recorded aggregate stock-based compensation expense related to the issuance of stock option awards to employees and non-employees in the statement of operations for the three and nine months ended September 30, 2017 and 2016 as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Research and development	$	40	$	4	$	107	$	7
General and administrative		14		—		81		—

Total stock-based compensation	$	54	$	4	$	188	$	7

Stock Options Granted to Employees. For the three and nine months ended September 30, 2017, the Company recorded $47 thousand and $78 thousand, respectively, of stock-based compensation expense related to employees’ stock options. For the three and nine months September 30, 2016, the Company had no employees. The fair value of options granted to employees was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions for the three and nine months ended September 30, 2017:


	Three months ended					Nine months ended
	September 30,					September 30,
	2017			2016		2017			2016
	(unaudited)					(unaudited)
Expected stock price volatility		80	%		—		80	%		—
Expected term of the award (years)		6.25			—		6.25			—
Risk-free interest rate		1.92	%		—		1.93	%		—
Exercise price	$	8.27			—	$	6.22			—
Estimated fair value of its Common Stock on the measurement date	$	8.27			—	$	8.46			—

There was $671 thousand of unrecognized stock-based compensation expense related to employees’ awards that is expected to be recognized over a weighted-average period of 3.26 years as of September 30, 2017.

Stock Options Granted to Non-Employees. Stock-based compensation expense related to stock options granted to non-employees is recognized as the stock options are earned. The Company believes that the estimated fair value of the stock options is more readily measurable than the fair value of the services rendered. For the three and nine months ended September 30, 2017, and three and nine months ended September 30, 2016, the Company recorded $7 thousand, $110 thousand, $4 thousand and $7 thousand, respectively, of stock-based compensation expense related to non-employees’ stock options.

The Company used the following weighted-average assumptions in estimating non-employees stock-based compensation expense:


	Three and nine months ended September 30, 2016
Expected stock price volatility		80	%
Expected term of the award (years)		6.25
Risk-free interest rate		1.97	%
Exercise price	$	2.46
Estimated fair value of its Common Stock on the measurement date	$	2.46

There were no options granted to non-employees in the nine months ended September 30, 2017.

Related Party Transactions

9 Months Ended

Sep. 30, 2017

Related Party Transactions

10.

Related Party Transactions

Convertible Promissory Notes

As of September 30, 2017 and December 31, 2016, the Company had balances of $0 and $698 thousand in related party convertible promissory notes, respectively (see Note 5).

Preferred Units

As of September 30, 2017 and December 31, 2016, the Company had outstanding balances of $0 and $1.4 million of preferred units, respectively. The preferred units as of December 31, 2016 were all held by the Chief Executive Officer and Chief Operating Officer of the Company as disclosed in Note 7.

Sale of Common Stock

On August 25, 2017, the Company closed the sale of 130,590 shares of Common Stock with an affiliate of a member of the Board for aggregate proceeds of $1.0 million.

In connection with our IPO, our Chief Executive Officer and Chief Operating Officer of the Company each purchased 100,000 shares of common stock at the offering price of $10 per share.

Subsequent Events

9 Months Ended

Sep. 30, 2017

Subsequent Events [Abstract]

Subsequent Events

11.

Subsequent Events

On November 1, 2017, the Company entered into a stock purchase agreement (the “Agreement”) with the Epidermolysis Bullosa Medical Research Foundation, a California nonprofit corporation (“EBMRF”), and EB Research Partnership, Inc., a New York not-for-profit corporation ( “EBRP” and together with EBMRF, the “Purchasers”), pursuant to which the Company has agreed to issue and sell, and the Purchasers have agreed to purchase, an aggregate of 70,000 shares of the Company’s common stock, par value $0.00001 per share, for a purchase price of $11.00 per share, resulting in aggregate gross proceeds to the Company of $770,000 (the “Transaction”). The offer, sale and issuance of the shares of the Company are exempt from registration pursuant to Rule 506 of Regulation D and Section 4(a)(2) of the Securities Act of 1933, as amended. Pursuant to the Agreement, the Purchasers have agreed they are acquiring the securities for investment only and not with a view to or for sale in connection with any distribution thereof and appropriate legends are to be affixed to the securities to be issued in conjunction with the Agreement. The Purchasers are subject to a six month lock-up, and the shares purchased under the terms of the Agreement will be subject to restrictions on selling, transferring or otherwise disposing of such shares. The Transaction closed on November 2, 2017.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2017

Accounting Policies [Abstract]

Basis of Presentation

Basis of Presentation

Unaudited Condensed Financial Information

Unaudited Condensed Financial Information

Use of Estimates

Use of Estimates

Segment and Geographical Information

Segment and Geographical Information

Concentrations of Credit Risk and Off-Balance Sheet Risk

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash

Cash

Cash consists of money market funds and bank deposit.

Deferred Issuance Costs

Deferred Issuance Costs

Fair Value of Financial Instruments

Fair Value of Financial Instruments

•

Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

•

Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly.

•

Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable.

Property and Equipment, net

Property and Equipment, net


Computer equipment and software			3 years
Lab equipment			3 years

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets

Convertible Preferred Stock

Convertible Preferred Stock

Research and Development Expenses

Research and Development Expenses

Stock-Based Compensation Expense

Stock-Based Compensation Expense

Net Loss Per Share Attributable to Common Stockholders and Members

Net Loss Per Share Attributable to Common Stockholders and Members

Comprehensive Loss

Comprehensive Loss

Recent Accounting Pronouncements

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2017

Accounting Policies [Abstract]

Summary of Estimated Useful Lives of Assets

Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows:


Computer equipment and software			3 years
Lab equipment			3 years

Property and Equipment, Net (Tables)

9 Months Ended

Sep. 30, 2017

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consist of the following (in thousands):


	September 30, 2017			December 31, 2016
	(unaudited)
Computer equipment and software	$	9		$	8
Laboratory equipment		57			7

Total property and equipment		66			15
Accumulated depreciation and amortization		(11	)		(2	)

Property and equipment, net	$	55			13

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2017

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Operating Lease Payments and Future Minimum Payments to be Received from Under Non-cancelable Subleases

As of September 30, 2017, future minimum operating lease payments and future minimum payments to be received from non-cancelable subleases were as follows (in thousands):


	Operating Leases
2017 (remaining three months)	$	28
2018		103
2019		—
2020		—
2021		—
Thereafter		—

Future minimum operating lease payments		131
Less: minimum payments to be received from non-cancelable subleases		(23	)

Total minimum lease payments, net	$	108

Capitalization (Tables)

9 Months Ended

Sep. 30, 2017

Equity [Abstract]

Schedule of Conversion of Notes into Preferred Stock

The following table outlines the conversion on August 8, 2017 of the Notes into shares of preferred stock (in thousands except share and per share amounts):


	Principal		Accrued Interest		Total		Conversion Price Per Share⁽¹⁾			Shares of Series A-1		Shares of Series A-2		Fair Value Date of Conversion		Fair Value Series A-1		Fair Value Series A-2		Loss on Extinguishment of Convertible Promissory Notes
Convertible promissory notes	$	2,444	$	72	$	2,516	$	4.14	⁽¹⁾		607,743		—	$	7.66	$	4,654	$	—	$	(2,138	)

Related party convertible promissory notes		948		32		980	$	4.14	⁽¹⁾		236,619		—	$	7.66		1,812		—		(832	)
Related party convertible promissory notes—June Note		750		8		758	$	6.13	⁽²⁾		—		123,691	$	7.66		—		947		(189	)

Total related party promissory notes		1,698		40		1,738					236,619		123,691				1,812		947		(1,021	)

Total	$	4,142	$	112	$	4,254					844,362		123,691			$	6,466	$	947	$	(3,159	)

(1)	The conversion price was determined by dividing the target valuation of $16 million by the outstanding shares of 3,863,547 immediately prior to the issuance of the Series A on August 8, 2017 (Note 4).

(2)	The conversion price was determined to be 80% of the $7.66 sales price per share of the Series A shares issued on August 8, 2017 (Note 5).

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

Schedule of Company's Stock Option Activity

The following table summarizes the Company’s stock option activity:


	Shares			Weighted- average Exercise Price		Weighted- average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (In thousands) ⁽¹⁾




Outstanding at January 1, 2016		—
Granted		142,105		$	2.46		9.7	$	—
Exercised		—
Cancelled or forfeited		—

Outstanding at December 31, 2016		142,105		$	2.46		9.7	$	338
Granted (unaudited)		71,649		$	6.22
Exercised (unaudited)		—			—
Cancelled or forfeited (unaudited)		(28,422	)	$	2.46

Outstanding at September 30, 2017 (unaudited)		185,332		$	3.91		9.3	$	1,122

Exercisable at September 30, 2017 (unaudited)		18,945		$	2.46		8.9	$	142

Vested at September 30, 2017 (unaudited)		18,945		$	2.46		8.9	$	142

(1)	The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at September 30, 2017 (unaudited) and December 31, 2016.

Summary of Stock Based Compensation Expense Related to Issuance of Stock Option Awards

The Company has recorded aggregate stock-based compensation expense related to the issuance of stock option awards to employees and non-employees in the statement of operations for the three and nine months ended September 30, 2017 and 2016 as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Research and development	$	40	$	4	$	107	$	7
General and administrative		14		—		81		—

Total stock-based compensation	$	54	$	4	$	188	$	7

Employee Stock Option [Member]

Fair Value of Stock Options, Valuation Assumptions

The fair value of options granted to employees was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions for the three and nine months ended September 30, 2017:


	Three months ended					Nine months ended
	September 30,					September 30,
	2017			2016		2017			2016
	(unaudited)					(unaudited)
Expected stock price volatility		80	%		—		80	%		—
Expected term of the award (years)		6.25			—		6.25			—
Risk-free interest rate		1.92	%		—		1.93	%		—
Exercise price	$	8.27			—	$	6.22			—
Estimated fair value of its Common Stock on the measurement date	$	8.27			—	$	8.46			—

Non-Employee Stock Option [Member]

Fair Value of Stock Options, Valuation Assumptions

The Company used the following weighted-average assumptions in estimating non-employees stock-based compensation expense:


	Three and nine months ended September 30, 2016
Expected stock price volatility		80	%
Expected term of the award (years)		6.25
Risk-free interest rate		1.97	%
Exercise price	$	2.46
Estimated fair value of its Common Stock on the measurement date	$	2.46

Organization - Additional Information (Detail) $ / shares in Units, $ in Thousands			9 Months Ended
	Sep. 22, 2017 USD ($) $ / shares shares	Sep. 14, 2017	Sep. 30, 2017 USD ($) shares	Sep. 19, 2017 shares	Mar. 31, 2017 shares	Dec. 31, 2016 USD ($) shares	Sep. 30, 2016 USD ($)
Organization And Basis Of Presentation [Line Items]
Stock split, conversion ratio		0.22222222
Forward stock split			1-to-4.5
Common stock, shares authorized \| shares			80,000,000	80,000,000,000	45,000,000,000	0
Convertible preferred stock, shares authorized \| shares			20,000,000	20,000,000,000		0
Accumulated deficit			$ (7,677)			$ (1,150)
Cash and cash equivalents			$ 52,570			$ 1,923	$ 398
IPO [Member]
Organization And Basis Of Presentation [Line Items]
Number of shares issued and sold \| shares	4,554,000,000
Shares issued, price per share \| $ / shares	$ 10.00
Underwriting discounts and commissions	$ 3,200
Proceeds from initial offering of shares	42,300
Offering expenses	1,500
Net proceeds from issuance of common stock, after deducting offering expenses	$ 40,800
Conversion of preferred stock to common stock \| shares	2,061,773,000
Preferred stock conversion basis			1-to-1
Over-Allotment Option [Member]
Organization And Basis Of Presentation [Line Items]
Number of shares issued and sold \| shares	594,000,000

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Assets (Detail)	9 Months Ended
	Sep. 30, 2017
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of assets	3 years

Summary of Significant Accounting Policies - Additional Information (Detail) - shares	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Preferred stock, shares outstanding	0	179,613,000	0

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 66	$ 15
Accumulated depreciation and amortization	(11)	(2)
Property and equipment, net	55	13
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	9	8
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 57	$ 7

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment, Net, by Type [Abstract]
Depreciation expense	$ 5	$ 0	$ 9	$ 1

Convertible Promissory Notes - Additional Information (Detail) - USD ($) shares in Thousands			3 Months Ended		9 Months Ended
	Aug. 08, 2017	Nov. 16, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Proceeds from preferred stock					$ 7,000,000	$ 754,000
Amount of notes outstanding			$ 0		$ 0		$ 1,800,000
Accrued interest							7,000
Sun Pharma Offering [Member]
Debt Instrument [Line Items]
Number of preferred shares issued upon debt conversion	360,311
Preferred stock conversion basis					1-to-1
IPO [Member]
Debt Instrument [Line Items]
Preferred stock conversion basis					1-to-1
Minimum [Member]
Debt Instrument [Line Items]
Proceeds from preferred stock					$ 5,000,000
Convertible Promissory Notes [Member] \| Note Purchase Agreement [Member]
Debt Instrument [Line Items]
Interest rate of debt		6.00%
Date of note purchase agreement		Nov. 16, 2016
Debt maturity month and Year		2018-05
Business combination, percentage of voting rights owned					50.00%
Target valuation amount	$ 16,000,000				$ 16,000,000
Conversion percentage					80.00%
Accrued interest			0		$ 0		$ 7,000
Interest expense			$ 32,000	$ 0	$ 106,000	$ 0
Convertible Promissory Notes [Member] \| Note Purchase Agreement [Member] \| Sun Pharma Offering [Member]
Debt Instrument [Line Items]
Number of preferred shares issued upon debt conversion	968,053

Related Party Convertible Promissory Notes - Additional Information (Detail) shares in Thousands					3 Months Ended		9 Months Ended
	Sep. 22, 2017 shares	Aug. 08, 2017 USD ($) shares	Jun. 06, 2017 USD ($)	Dec. 27, 2016 USD ($) RelatedParty	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	May 17, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 14, 2016 USD ($)
Debt Instrument [Line Items]
Convertible promissory note amount					$ 0		$ 0			$ 698,000
Accrued Interest		$ 112,000
Sun Pharma Offering [Member]
Debt Instrument [Line Items]
Accrued Interest		$ 40,000
Preferred shares issued upon conversion \| shares		360,311
Conversion of preferred stock to common stock \| shares	2,061,773
Preferred stock conversion basis							1-to-1
Convertible Promissory Notes [Member] \| Agreements - Related Parties [Member]
Debt Instrument [Line Items]
Accrued Interest		$ 40,000			0		$ 0			$ 2,000
Interest expense					$ 12,000	$ 0	$ 37,000	$ 0
Convertible Promissory Notes [Member] \| Note Purchase Agreement - Related Parties [Member]
Debt Instrument [Line Items]
Accrued Interest		$ 32,000
Convertible Promissory Notes [Member] \| Note Purchase Agreement - Related Parties [Member] \| Director [Member]
Debt Instrument [Line Items]
Convertible promissory note amount									$ 250,000		$ 250,000
Convertible Promissory Notes [Member] \| Note Purchase Agreement - Related Parties [Member] \| Executive Officer [Member]
Debt Instrument [Line Items]
Convertible promissory note amount				$ 448,000
Number of related party \| RelatedParty				2
Convertible Promissory Notes [Member] \| Second Note Purchase Agreement - Related Parties [Member]
Debt Instrument [Line Items]
Conversion percentage		80.00%					80.00%
Business combination, percentage of voting rights owned							80.00%
Accrued Interest		$ 8,000
Convertible Promissory Notes [Member] \| Second Note Purchase Agreement - Related Parties [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Conversion of convertible securities							$ 5,000,000
Convertible Promissory Notes [Member] \| Second Note Purchase Agreement - Related Parties [Member] \| Director [Member]
Debt Instrument [Line Items]
Convertible promissory note amount			$ 750,000
Convertible promissory note, interest rate			6.00%
Debt maturity month and Year			2018-05

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Installment	Sep. 30, 2016 USD ($)
Operating Leased Assets [Line Items]
Rent expense \| $	$ 20	$ 24	$ 59	$ 35
2016 Lease Agreement [Member]
Operating Leased Assets [Line Items]
Lease expiration date			Oct. 31, 2017
First Amendment to 2016 Lease Agreements [Member]
Operating Leased Assets [Line Items]
Number of installments \| Installment			17
Second Amendment to 2016 Lease Agreement [Member]
Operating Leased Assets [Line Items]
Lease expiration date			Oct. 31, 2018

Commitments and Contingencies - Schedule of Future Minimum Operating Lease Payments and Future Minimum Payments to be Received from Under Non-cancelable Subleases (Detail) $ in Thousands	Sep. 30, 2017 USD ($)
Leases, Operating [Abstract]
2017 (remaining three months)	$ 28
2018	103
2019	0
2020	0
2021	0
Thereafter	0
Future minimum operating lease payments	131
Less: minimum payments to be received from non-cancelable subleases	(23)
Total minimum lease payments, net	$ 108

Capitalization - Additional Information (Detail) - USD ($)								1 Months Ended	9 Months Ended
	Sep. 22, 2017	Aug. 25, 2017	Aug. 08, 2017	Aug. 04, 2017	Dec. 27, 2016	Sep. 30, 2016	Apr. 15, 2016	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 19, 2017	Mar. 31, 2017	Dec. 31, 2016
Schedule of Capitalization, Equity [Line Items]
Stock conversion rate												100.00%	100.00%
Preferred stock, shares authorized												450,000,000
Preferred stock, par value				$ 0.00001								$ 0.00001
Preferred stock, shares issued												179,613,000
Preferred stock, shares outstanding								0	0			179,613,000	0
Common stock, shares authorized								80,000,000	80,000,000		80,000,000,000	45,000,000,000	0
Common stock, par value				$ 0.00001				$ 0.00001	$ 0.00001			$ 0.00001	$ 0.00001
Common stock, shares issued								10,237,247	10,237,247			3,490,884,000	0
Common shares, shares outstanding								10,237,247	10,237,247			3,490,884,000	0
Common units, outstanding								0	0				3,490,884
Preferred units, outstanding								0	0				179,613
Common stock, additional shares authorized				1,500,000,000
Preferred stock, additional shares authorized				1,500,000,000
Aggregate proceeds from issuance of preferred stock									$ 7,000,000	$ 754,000
Proceeds from issue of common stock									$ 43,162,000	$ 100,000
Preferred units, authorized							100,000
Preferred units, issued					70,497,000		450,000	96,345,000	96,345,000
Proceeds from issuance of preferred units					$ 552,000		$ 100,000	$ 754,000
Stock conversion price								$ 7.83	$ 7.83
Stock conversion description									On March 31, 2017, all of the preferred units were converted into preferred stock on a 1-to-1 basis.
Preferred units, outstanding								$ 0	$ 0				$ 1,406,000
Preferred stock, voting rights									The holders of shares of preferred stock are entitled to one vote for each share of preferred stock held
Preferred stock dividend, declared or paid									$ 0
Common stock, voting rights									The holders of shares of common stock are entitled to one vote for each share of common stock held
Common stock dividend, declared or paid									$ 0
Series Seed Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred stock, additional shares authorized				179,613,000
Series A Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Shares issued, price per share			$ 7.66
Preferred stock, additional shares authorized				210,000,000
Series A 1 Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred stock, additional shares authorized				200,000,000
Series A 2 Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred stock, additional shares authorized				30,000,000
Preferred Units [Member]
Schedule of Capitalization, Equity [Line Items]
Conversion of stock, units converted								12,771,000
Common Units [Member]
Schedule of Capitalization, Equity [Line Items]
Conversion of stock, units converted						3,490,884,000		3,490,884,000
Director [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold		130,590,000
Shares issued, price per share		$ 7.66
Proceeds from issue of common stock		$ 1,000,000
IPO [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold	4,554,000,000
Shares issued, price per share	$ 10.00
Underwriting discounts and commissions	$ 3,200,000
Proceeds from initial offering of shares	42,300,000
Offering expenses	1,500,000
Net proceeds from issuance of common stock, after deducting offering expenses	$ 40,800,000
Conversion of preferred stock to common stock	2,061,773,000
Preferred stock conversion basis									1-to-1
Over-Allotment Option [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold	594,000,000
Sun Pharma Offering [Member]
Schedule of Capitalization, Equity [Line Items]
Conversion of preferred stock to common stock	2,061,773,000
Preferred stock conversion basis									1-to-1
Sun Pharma Offering [Member] \| Series A Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred stock, shares issued			914,107,000
Shares issued, price per share			$ 7.66
Aggregate proceeds from issuance of preferred stock			$ 7,000,000

Capitalization - Schedule of Mandatory Conversion of Notes into Preferred Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended
	Aug. 08, 2017	Sep. 30, 2017	Dec. 31, 2016
Debt Conversion [Line Items]
Principal	$ 4,142
Accrued Interest	112
Total	4,254
Fair Value Preferred Stock		$ 4,142
Loss on Extinguishment of Convertible Promissory Notes	(3,159)
Convertible Promissory Notes [Member] \| Note Purchase Agreement [Member]
Debt Conversion [Line Items]
Principal	2,444
Accrued Interest	72
Total	$ 2,516
Conversion Price Per Share	$ 4.14
Fair Value Date of Conversion	$ 7.66
Loss on Extinguishment of Convertible Promissory Notes	$ (2,138)
Convertible Promissory Notes [Member] \| Note Purchase Agreement - Related Parties [Member]
Debt Conversion [Line Items]
Principal	948
Accrued Interest	32
Total	$ 980
Conversion Price Per Share	$ 4.14
Fair Value Date of Conversion	$ 7.66
Loss on Extinguishment of Convertible Promissory Notes	$ (832)
Convertible Promissory Notes [Member] \| Second Note Purchase Agreement - Related Parties [Member]
Debt Conversion [Line Items]
Principal	750
Accrued Interest	8
Total	$ 758
Conversion Price Per Share	$ 6.13
Fair Value Date of Conversion	$ 7.66
Loss on Extinguishment of Convertible Promissory Notes	$ (189)
Convertible Promissory Notes [Member] \| Agreements - Related Parties [Member]
Debt Conversion [Line Items]
Principal	1,698
Accrued Interest	40	$ 0	$ 2
Total	1,738
Loss on Extinguishment of Convertible Promissory Notes	$ (1,021)
Series A 1 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	844,362
Fair Value Preferred Stock	$ 6,466
Series A 1 Preferred Stock [Member] \| Convertible Promissory Notes [Member] \| Note Purchase Agreement [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	607,743
Fair Value Preferred Stock	$ 4,654
Series A 1 Preferred Stock [Member] \| Convertible Promissory Notes [Member] \| Note Purchase Agreement - Related Parties [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	236,619
Fair Value Preferred Stock	$ 1,812
Series A 1 Preferred Stock [Member] \| Convertible Promissory Notes [Member] \| Agreements - Related Parties [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	236,619
Fair Value Preferred Stock	$ 1,812
Series A 2 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	123,691
Fair Value Preferred Stock	$ 947
Series A 2 Preferred Stock [Member] \| Convertible Promissory Notes [Member] \| Second Note Purchase Agreement - Related Parties [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	123,691
Fair Value Preferred Stock	$ 947
Series A 2 Preferred Stock [Member] \| Convertible Promissory Notes [Member] \| Agreements - Related Parties [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	123,691
Fair Value Preferred Stock	$ 947

Capitalization - Schedule of Mandatory Conversion of Notes into Preferred Stock (Parenthetical) (Detail) - USD ($)		9 Months Ended
	Aug. 08, 2017	Sep. 30, 2017
Series A Preferred Stock [Member]
Debt Conversion [Line Items]
Shares issued, price per share	$ 7.66
Note Purchase Agreement [Member] \| Convertible Promissory Notes [Member]
Debt Conversion [Line Items]
Target valuation amount	$ 16,000,000	$ 16,000,000
Number of outstanding shares used for calculation of conversion price	3,863,547
Conversion percentage		80.00%
Note Purchase Agreement - Related Parties [Member] \| Convertible Promissory Notes [Member]
Debt Conversion [Line Items]
Target valuation amount	$ 16,000,000
Number of outstanding shares used for calculation of conversion price	3,863,547
Second Note Purchase Agreement - Related Parties [Member] \| Convertible Promissory Notes [Member]
Debt Conversion [Line Items]
Conversion percentage	80.00%	80.00%

Significant Agreements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses incurred	$ 1,355	$ 241	$ 2,120	$ 339
Clinical Supply Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated remaining commitment	1,700		1,700
Expenses incurred	$ 483	$ 0	$ 643	$ 0

Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($) shares	Mar. 31, 2017 shares	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($) Employee	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) Employee	Dec. 31, 2016 shares	Sep. 05, 2017 shares	Oct. 01, 2016 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period					4 years
Stock option expiration period					10 years
Options to purchase of shares of common stock	185,332,000		185,332,000		185,332,000		142,105,000
Stock options granted					71,649,000		142,105,000
Stock-based compensation expense \| $			$ 54	$ 4	$ 188	$ 7
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $			40	$ 4	$ 107	$ 7
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value of options granted \| $ / shares					$ 6.42
Stock-based compensation expense \| $			47		$ 78
Number of employees \| Employee				0		0
Unrecognized stock-based compensation expense \| $	$ 671		671		$ 671
Estimated weighted average period	3 years 3 months 4 days
Non-Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted under the plan					0
Non-Employee Stock Option [Member] \| Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $			$ 7	$ 4	$ 110	$ 7
2016 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorization to issue number of common stock									189,472,000
Stock option vesting period					4 years
Stock option expiration period					10 years
Number of shares granted under the plan		113,683,000
Options to purchase of shares of common stock		0
2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorization to issue number of common stock		193,050,000
Stock option vesting period					4 years
Stock option expiration period					10 years
Options to purchase of shares of common stock		113,683,000
2017 IPO Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorization to issue number of common stock								900,000
Shares of common stock available for future grants	900,000,000		900,000,000		900,000,000

Stock-Based Compensation - Schedule of Company's Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares outstanding, beginning balance \| shares	142,105
Weighted-average remaining contractual life (years), granted		9 years 8 months 12 days
Shares, granted \| shares	71,649	142,105
Shares, exercised \| shares	0	0
Shares, cancelled or forfeited \| shares	(28,422)
Shares outstanding, ending balance \| shares	185,332	142,105
Weighted-average exercise price outstanding, beginning balance \| $ / shares	$ 2.46
Shares exercisable at September 30, 2017 \| shares	18,945
Weighted-average exercise price, granted \| $ / shares	$ 6.22	$ 2.46
Shares vested at September 30, 2017 \| shares	18,945
Weighted-average exercise price, exercised \| $ / shares	$ 0
Weighted-average exercise price, cancelled or forfeited \| $ / shares	2.46
Weighted-average exercise price outstanding, ending balance \| $ / shares	3.91	$ 2.46
Weighted-average exercise price exercisable at September 30, 2017 \| $ / shares	2.46
Weighted-average exercise price vested at September 30, 2017 \| $ / shares	$ 2.46
Weighted-average remaining contractual life (years), outstanding	9 years 3 months 19 days	9 years 8 months 12 days
Weighted-average remaining contractual life (years), exercisable	8 years 10 months 25 days
Weighted-average remaining contractual life (years), vested	8 years 10 months 25 days
Aggregate intrinsic value, outstanding \| $	$ 1,122	$ 338
Aggregate intrinsic value, exercisable \| $	142
Aggregate intrinsic value, vested \| $	$ 142

Stock-Based Compensation - Summary of Stock Based Compensation Expense Related to Issuance of Stock Option Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 54	$ 4	$ 188	$ 7
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	40	$ 4	107	$ 7
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 14		$ 81

Stock-Based Compensation - Fair Value of Stock Options, Valuation Assumptions (Detail) - $ / shares	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price		$ 6.22		$ 2.46
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected stock price volatility	80.00%	80.00%
Expected term of the award (years)	6 years 2 months 30 days	6 years 2 months 30 days
Risk-free interest rate	1.92%	1.93%
Exercise price	$ 8.27	$ 6.22
Estimated fair value of its Common Stock on the measurement date	$ 8.27	$ 8.46
Non-Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected stock price volatility			80.00%
Expected term of the award (years)			6 years 2 months 30 days
Risk-free interest rate			1.97%
Exercise price			$ 2.46
Estimated fair value of its Common Stock on the measurement date			$ 2.46

Related Party Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			9 Months Ended
	Sep. 22, 2017	Aug. 25, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Related party convertible promissory notes			$ 0		$ 698
Preferred units, outstanding			0		1,406
Proceeds from sale of common stock			$ 43,162	$ 100
IPO [Member]
Related Party Transaction [Line Items]
Number of shares issued and sold	4,554,000,000
Shares issued, price per share	$ 10.00
Chief Executive Officer [Member] \| IPO [Member]
Related Party Transaction [Line Items]
Number of shares issued and sold			100,000
Shares issued, price per share			$ 10
Chief Operating Officer [Member] \| IPO [Member]
Related Party Transaction [Line Items]
Number of shares issued and sold			100,000
Shares issued, price per share			$ 10
Chief Executive Officer and Chief Operating Officer [Member]
Related Party Transaction [Line Items]
Preferred units, outstanding					$ 1,400
Director [Member]
Related Party Transaction [Line Items]
Number of shares issued and sold		130,590,000
Proceeds from sale of common stock		$ 1,000

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		9 Months Ended
	Nov. 01, 2017	Sep. 30, 2017	Sep. 30, 2016	Aug. 04, 2017	Mar. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Common stock, par value		$ 0.00001		$ 0.00001	$ 0.00001	$ 0.00001
Aggregate gross proceeds		$ 43,162	$ 100
Subsequent Event [Member] \| Stock Purchase Agreement [Member]
Subsequent Event [Line Items]
Number of shares issued and sold	70,000
Common stock, par value	$ 0.00001
Shares issued, price per share	$ 11.00
Aggregate gross proceeds	$ 770,000