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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	KRYS
Entity Registrant Name	Krystal Biotech, Inc.
Entity Central Index Key	0001711279
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		10,307,247
Entity Public Float			$ 0

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash	$ 49,591	$ 1,923
Prepaid assets	304	246
Other current assets	19
Total current assets	49,914	2,169
Property and equipment, net	200	13
Total assets	50,114	2,182
Current liabilities
Accounts payable	193	42
Accrued expenses and other current liabilities	447	1
Total current liabilities	640	43
Accrued interest	0	7
Related party convertible promissory notes	0	698
Convertible promissory notes		1,145
Total liabilities	640	1,893
Commitments and contingencies (Note 7)
Preferred stock
Preferred stock	0	0
Stockholders' and members’ equity
Common stock; $0.00001 par value; 80,000,000 shares authorized, 10,307,247 shares issued and outstanding at December 31, 2017; no shares authorized, issued, or outstanding at December 31, 2016	0	0
Common units; no par value; no common units authorized, issued, or outstanding at December 31, 2017; 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 December 31, 2017; 179,613 units authorized, issued, and outstanding at December 31, 2016 (aggregate liquidation preference of $1,406)	0	1,406
Additional paid-in capital	58,544	33
Accumulated deficit	(9,070)	(1,150)
Total stockholders' and members’ equity	49,474	289
Total liabilities, convertible preferred stock and stockholders' and members’ equity	50,114	2,182
Preferred Stock [Member]
Preferred stock
Preferred stock	$ 0	$ 0

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 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	10,307,247	0
Common stock, shares outstanding	10,307,247	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

Statements of Operations - USD ($) $ in Thousands	12 Months Ended
Statements of Operations - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Expenses
Research and development	$ 3,208	$ 741
General and administrative	1,564	402
Total operating expenses	4,772	1,143
Loss from operations	(4,772)	(1,143)
Other Expense
Interest and other expense, net	(3,148)	(7)
Total other expense	(3,148)	(7)
Net loss	(7,920)	(1,150)
Net loss applicable to stockholders and members	$ (7,920)	$ (1,150)
Net loss attributable to common stockholders per share:
Basic and diluted	$ (1.48)	$ (1.31)
Weighted-average common shares and common units outstanding
Basic and diluted	5,360,536	877,490

Statements of Convertible Preferred Stock, Stockholders' and Members' Equity - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Common Units [Member]	Preferred Units [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2015
Beignning balance, shares at Dec. 31, 2015
Beginning Balance at Dec. 31, 2015
Begining Balance, shares at Dec. 31, 2015
Issuance of common units/shares	100		$ 100
Issuance of common stock, shares			450
Conversion from common units to preferred units			$ (100)	$ 100
Conversion from common units to preferred units, shares			(450)	12,771
Issuance of preferred and common units	1,306			$ 1,306
Issuance of preferred and common units, shares			3,490,884	166,842
Stock-based compensation expense	33					33
Net loss	(1,150)						(1,150)
Ending balance at Dec. 31, 2016	$ 289			$ 1,406		33	(1,150)
Ending Balance, shares at Dec. 31, 2016	0
Ending Balance at Dec. 31, 2016	$ 0	0
Ending Balance, shares at Dec. 31, 2016			3,490,884	179,613
Conversion of preferred units to preferred stock	(1,406)	$ 1,406
Conversion of preferred units to preferred stock, shares		179,613
Conversion of preferred units to preferred stock, shares				(179,613)
Conversion of preferred units to preferred stock				$ (1,406)
Conversion of common units to common stock, shares			(3,490,884)		3,490,884
Conversion of convertible promissory notes to preferred stock	3,158					3,158
Conversion of convertible promissory notes to preferred stock, shares		968,053
Conversion of convertible promissory notes to preferred stock		$ 4,255
Issuance of preferred stock		$ 7,000
Issuance of preferred stock, shares		914,107
Issuance of common units/shares	42,446					42,446
Issuance of common stock, shares					4,754,590
Conversion of preferred stock to common stock	12,661					12,661
Conversion of preferred stock to common stock, shares		(2,061,773)
Conversion of preferred stock to common stock		$ (12,661)
Conversion of preferred stock to common stock, shares					2,061,773
Stock-based compensation expense	246					246
Net loss	(7,920)						(7,920)
Ending balance at Dec. 31, 2017	$ 49,474					$ 58,544	$ (9,070)
Ending Balance, shares at Dec. 31, 2017	0
Ending Balance at Dec. 31, 2017	$ 0	$ 0
Ending Balance, shares at Dec. 31, 2017					10,307,247

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net loss	$ (7,920)	$ (1,150)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	23	2
Stock-based compensation expense	246	33
Non-cash interest expense	3,263	7
(Increase) decrease in
Prepaid and other assets	(77)	(246)
Accounts payable	133	42
Accrued expenses and other current liabilities	442	1
Net cash used in operating activities	(3,890)	(1,311)
Investing Activities
Purchases of property and equipment	(210)	(15)
Net cash used in investing activities	(210)	(15)
Financing Activities
Proceeds from the issuance of convertible promissory notes	1,299	1,145
Proceeds from the issuance of related party convertible promissory notes	1,000	698
Issuance of common stock and common units, net	42,469	100
Issuance of preferred stock and preferred units	7,000	1,306
Net cash provided by financing activities	51,768	3,249
Net increase in cash	47,668	1,923
Cash at beginning of period	1,923
Cash at end of period	49,591	1,923
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	$ 23

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

Basis of Presentation

The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the 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 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 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 deposits.

Deferred Issuance Costs

Deferred public offering costs, which consist primarily of direct, incremental legal and accounting fees relating to the IPO, are offset against IPO proceeds at December 31, 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 are unobservable.

To the extent that a 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 within 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 years ended December 31, 2017 and 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 years ended December 31, 2017 and 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 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 for the years ended December 31, 2017 and 2016.

Convertible Preferred Stock

In accordance with the guidance in FASB ASC Topic 480, Distinguishing Liabilities from Equity, shares of preferred stock (Note 8), 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 December 31, 2017 and 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 sufficient history and trading volume 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 mean 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 financial statements is based on awards that are ultimately expected to vest.

Income Taxes

For the year ended December 31, 2016, the Company was organized in the State of California as a LLC and was taxed as a partnership for United States income tax purposes and therefore filed federal and state flow-through income tax returns. As a result, no U.S. current or deferred income tax assets or liabilities are reflected in the December 31, 2016 financial statements. The Company’s members are obligated to report that member’s proportionate share of the Company’s taxable income or loss.

For the year ended December 31, 2017 income taxes are recorded in accordance with FASB ASC Topic 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. Under this method, we record deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect when the differences are expected to reverse. Valuation allowances are provided when necessary to reduce net deferred tax assets to the amount that is more likely than not to be realized. Based on the available evidence, we are unable, at this time, to support the determination that it is more likely than not that our deferred tax assets will be utilized in the future. Accordingly, we recorded a full valuation allowance as of December 31, 2017. We intend to maintain valuation allowances until sufficient evidence exists to support their reversal.

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

The Company may recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2017 and 2016, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations.

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 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 years ended December 31, 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 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 financial statements and related disclosures.

Capitalization

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Capitalization

8.	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

On September 22, 2017, the Company completed its IPO 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 $1.6 million, net proceeds to the Company were approximately $40.7 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.

Sale 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.

On November 1, 2017, the Company entered into a stock purchase agreement (the “Agreement”) with the Epidermolysis Bullosa Medical Research Foundation, a California not-for-profit 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 Company intends to commence work on or before September 1, 2018 and to use the proceeds exclusively to complete the research plan pursuant to the Agreement. There is a redemption feature whereby the Company shall repurchase all or a portion of the shares at a purchase price of $11.00 per share or the closing trading price of the common stock on the redemption request date, whichever is higher, should the Company not commence work on or before September 1, 2018 or cease commercially reasonable efforts. As the redemption feature is within the control of the Company, the common stock issued pursuant to this Agreement is classified as permanent equity. 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.

Shares Outstanding

As of December 31, 2017, 10,307,247 shares of common stock were outstanding. As of December 31, 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 5), all outstanding Notes plus accrued interest thereon were automatically converted into shares of preferred stock. As the conversion price per share of preferred stock was lower than the market price of each share of preferred stock on the date of conversion, an interest expense of $3.2 million was recorded upon conversion representing this beneficial conversion feature.

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 5).

(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 6).

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 December 31, 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 December 31, 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 December 31, 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 December 31, 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 December 31, 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.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased 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 authorized 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, 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, however vesting provisions can vary by award based on the discretion of the Board. 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, however 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. 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 years ended December 31, 2017 and 2016, respectively, to employees, consultants and member of the Board, 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:

						Weighted-
				Weighted-		average		Aggregate
				average		Remaining		Intrinsic
				Exercise		Contractual		Value
	Shares			Price		Life (Years)		(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		71,649		$	6.22
Exercised		—			—
Cancelled or forfeited		(28,422	)	$	2.46

Outstanding at December 31, 2017		185,332		$	3.91		9.0		1,224

Exercisable at December 31, 2017		43,221		$	2.46		8.7	$	348

Vested at December 31, 2017		43,221		$	2.46		8.7	$	348

(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 December 31, 2017 and December 31, 2016.

As of December 31, 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 year ended December 31, 2017 was $6.42.

Stock-based compensation expense for the years ended December 31, 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 year ended December 31, 2017 and 2016 as follows (in thousands):

	Year Ended December 31,
	2017		2016
Research and development	$	151	$	25
General and administrative		95		8
Total stock-based compensation	$	246	$	33

Stock Options Granted to Employees. For the and years ended December 31, 2017 and 2016, the Company recorded $130 thousand and $3 thousand, respectively, of stock-based compensation expense related to employees’ stock options. For the year ended December 31, 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 years ended December 31, 2017 and 2016:

	Year Ended December 31,
	2017			2016
Expected stock price volatility		80	%		—
Expected term of the award (years)		6.25			—
Risk-free interest rate		1.93	%		—
Exercise price	$	6.22			—

There was $623 thousand of unrecognized stock-based compensation expense related to employees’ awards that is expected to be recognized over a weighted-average period of 3.0 years as of December 31, 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 year ended December 31, 2017 and 2016, the Company recorded $116 thousand and $30 thousand, respectively, of stock-based compensation expense related to non-employees’ stock options.

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

	Year Ended December 31,
	2017		2016
Expected stock price volatility		—		80	%
Expected term of the award (years)		—		6.25
Risk-free interest rate		—		1.97	%
Exercise price		—	$	2.46

There was $93 thousand of unrecognized stock-based compensation expense related to non-employees’ awards that is expected to be recognized over a weighted-average period of 2.9 years as of December 31, 2017.

There were no options granted to non-employees in the year ended December 31, 2017.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

10.	Income Taxes

From inception through December 31, 2016, the Company was a California LLC for federal and state income tax purposes, and therefore, all items of income or loss through December 31, 2016 flowed through to the members of the LLC. Effective January 1, 2017, the Company converted from an LLC to a C-corporation for federal and state income tax purposes. Prior to the conversion to a C-corporation, the Company did not record deferred tax assets or liabilities or have any net operating loss (“NOL”) carryforwards for federal income tax purposes. Effective upon the conversion to a C-corporation, the Company became subject to income tax at the federal and state levels.

We did not record a current or deferred income tax expense or benefit for the years ended December 31, 2017 and 2016. As we were an LLC for the year ended December 31, 2016, we were not subject to federal income tax. A reconciliation of income tax expense (benefit) computed at the statutory federal and state income tax rate of 28% for the year to income tax expense (benefit) as reflected in our financial statements for years ended December 31, 2017 and 2016 are as follows (in thousands):

	December 31,
	2017
Federal income tax expense (benefit) at statutory rate	$	(2,693	)
Change in valuation allowance		2,164
Impact of US tax reform		1,022
State income tax expense net of federal benefit		(514	)
Other non-deductible expenses		21
Total tax expense (benefit)	$	—

The significant components of the Company’s deferred tax assets as of December 31, 2017 are as follows (in thousands):

	December 31,
	2017
Deferred tax assets:
Net operating loss carryforwards	$	2,029
Non-qualified option		29
Depreciation		(31	)
Accrued expenses		137
Total deferred tax assets		2,164
Valuation allowance		(2,164	)
Net deferred tax assets	$	—

The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of operating losses, the Company has concluded that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2017.

As of December 31, 2016, the Company had U.S. federal NOL carryforwards of approximately $0 as the company was a flow-through entity. As of December 31, 2017, the Company had U.S. federal NOL carryforwards of approximately $7.4 million which may be available to offset future income tax liabilities and expire at various dates through 2037.

Under the provisions of the Internal Revenue Code, the NOL carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOL carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future.

Under 2017 Tax Cuts and Jobs Act, NOL deductions for NOLs arising in the tax years beginning after December 31, 2017 will be limited to 80% of taxable income and NOL carrybacks will be eliminated.

The Company files income tax returns in the United States at the federal level and in states in which the Company conducts business activities. The federal and state income tax returns are generally subject to tax examinations for the tax year ended December 31, 2017. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service or state tax authorities to the extent utilized in a future period.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Segment and Geographical Information

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash

Cash consists of money market funds and bank deposits.

Deferred Issuance Costs

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

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 are unobservable.

Property and Equipment, net


Computer equipment and software			3 years
Lab equipment			3 years

Impairment of Long-Lived Assets

Convertible Preferred Stock

Research and Development Expenses

Stock-Based Compensation Expense

Income Taxes

Comprehensive Loss

Recent Accounting Pronouncements

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2017

Balance Sheet Components [Abstract]

Schedule of Property and Equipment, Net

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

	December 31,
	2017			2016
Computer equipment and software	$	11		$	8
Laboratory equipment		214			7
Total property and equipment		225			15
Accumulated depreciation and amortization		(25	)		(2	)
Property and equipment, net	$	200		$	13

Schedule of Accrued Expenses And Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):

	December 31,
	2017		2016
Accrued pre-clinical expenses	$	257	$	—
Accrued Professional fees		77		—
Accrued payroll and benefits		10		—
Accrued taxes		103		1
Total	$	447	$	1

Capitalization (Tables)

12 Months Ended

Dec. 31, 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 5).

(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 6).

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Company's Stock Option Activity

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

						Weighted-
				Weighted-		average		Aggregate
				average		Remaining		Intrinsic
				Exercise		Contractual		Value
	Shares			Price		Life (Years)		(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		71,649		$	6.22
Exercised		—			—
Cancelled or forfeited		(28,422	)	$	2.46

Outstanding at December 31, 2017		185,332		$	3.91		9.0		1,224

Exercisable at December 31, 2017		43,221		$	2.46		8.7	$	348

Vested at December 31, 2017		43,221		$	2.46		8.7	$	348

(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 December 31, 2017 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 year ended December 31, 2017 and 2016 as follows (in thousands):

	Year Ended December 31,
	2017		2016
Research and development	$	151	$	25
General and administrative		95		8
Total stock-based compensation	$	246	$	33

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 years ended December 31, 2017 and 2016:

	Year Ended December 31,
	2017			2016
Expected stock price volatility		80	%		—
Expected term of the award (years)		6.25			—
Risk-free interest rate		1.93	%		—
Exercise price	$	6.22			—

Non-Employee Stock Option [Member]

Fair Value of Stock Options, Valuation Assumptions

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

	Year Ended December 31,
	2017		2016
Expected stock price volatility		—		80	%
Expected term of the award (years)		—		6.25
Risk-free interest rate		—		1.97	%
Exercise price		—	$	2.46

Organization - Additional Information (Detail) $ / shares in Units, $ in Thousands			12 Months Ended
	Sep. 22, 2017 USD ($) $ / shares shares	Sep. 05, 2017	Dec. 31, 2017 USD ($) shares	Sep. 19, 2017 shares	Mar. 31, 2017 shares	Dec. 31, 2016 USD ($) shares
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	45,000,000	0
Convertible preferred stock, shares authorized \| shares			20,000,000	20,000,000		0
Accumulated deficit			$ (9,070)			$ (1,150)
Cash and cash equivalents			$ 49,591			$ 1,923
IPO [Member]
Organization And Basis Of Presentation [Line Items]
Number of shares issued and sold \| shares	4,554,000
Shares issued, price per share \| $ / shares	$ 10.00
Underwriting discounts and commissions	$ 3,200
Proceeds from initial offering of shares	42,300
Offering expenses	1,600
Net proceeds from issuance of common stock, after deducting offering expenses	$ 40,700
Conversion of preferred stock to common stock \| shares	2,061,773
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

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) Segment shares	Dec. 31, 2016 USD ($) shares	Mar. 31, 2017 shares
Significant Accounting Policies [Line Items]
Number of operating segment \| Segment	1
Number of geographic segment \| Segment	1
Recognized impairment losses for long lived assets	$ 0	$ 0
Preferred stock, shares outstanding \| shares	0	0	179,613
Accrued interest or penalties related to uncertain tax positions	$ 0	$ 0
Recognized income tax benefit	$ 0	0
State of California [Member]
Significant Accounting Policies [Line Items]
U.S. current income tax		0
Deferred income tax assets		0
Deferred income tax liabilities		$ 0

Convertible Promissory Notes - Additional Information (Detail) - USD ($)			12 Months Ended
	Aug. 08, 2017	Nov. 16, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Proceeds from preferred stock			$ 7,000,000	$ 1,306,000
Amount of notes outstanding			0	1,800,000
Accrued interest			0	7,000
Minimum [Member]
Debt Instrument [Line Items]
Proceeds from preferred stock			$ 5,000,000
IPO [Member]
Debt Instrument [Line Items]
Preferred stock conversion basis			1-to-1
Sun Pharma Offering [Member]
Debt Instrument [Line Items]
Preferred stock conversion basis			1-to-1
Number of preferred shares issued upon debt conversion	360,311
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%
Interest expense			$ 106,000	$ 7,000
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)				12 Months Ended
	Sep. 22, 2017 shares	Aug. 08, 2017 USD ($) shares	Dec. 27, 2016 USD ($) RelatedParty	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 06, 2017 USD ($)	May 17, 2017 USD ($)	Nov. 14, 2016 USD ($)
Debt Instrument [Line Items]
Convertible promissory note amount				$ 0	$ 698,000
Conversion of preferred stock to common stock				$ 12,661,000
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] \| 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 preferred stock to common stock				$ 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%
Convertible Promissory Notes [Member] \| Agreements - Related Parties [Member]
Debt Instrument [Line Items]
Accrued Interest		$ 40,000		0	2,000
Interest expense				$ 37,000	$ 2,000

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	Dec. 31, 2017 USD ($)
Leases Operating [Abstract]
2018	$ 102
2019	0
2020	0
2021	0
2022	0
Thereafter	0
Future minimum operating lease payments	102
Less: minimum payments to be received from non-cancelable subleases	(18)
Total minimum lease payments, net	$ 84

Capitalization - Additional Information (Detail) - USD ($)								1 Months Ended	12 Months Ended
	Nov. 01, 2017	Sep. 22, 2017	Aug. 25, 2017	Aug. 08, 2017	Aug. 04, 2017	Dec. 27, 2016	Apr. 15, 2016	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Sep. 19, 2017	Mar. 31, 2017
Schedule of Capitalization, Equity [Line Items]
Stock conversion rate												100.00%
Preferred stock, shares authorized												450,000
Preferred stock, par value					$ 0.00001							$ 0.00001
Preferred stock, shares issued												179,613
Preferred stock, shares outstanding								0	0	0		179,613
Common stock, shares authorized								80,000,000	80,000,000	0	80,000,000	45,000,000
Common stock, par value					$ 0.00001			$ 0.00001	$ 0.00001	$ 0.00001		$ 0.00001
Common stock, shares issued								10,307,247	10,307,247	0		3,490,884
Common shares, shares outstanding								10,307,247	10,307,247	0		3,490,884
Proceeds from issue of common stock									$ 42,469,000	$ 100,000
Common units, outstanding								0	0	3,490,884
Preferred units, outstanding								0	0	179,613
Common stock, additional shares authorized					1,500,000
Preferred stock, additional shares authorized					1,500,000
Aggregate proceeds from issuance of preferred stock									$ 7,000,000	$ 1,306,000
Preferred units, authorized							100
Preferred units, issued						70,497	450	96,345	96,345
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
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
Series A 1 Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred stock, additional shares authorized					200,000
Series A 2 Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred stock, additional shares authorized					30,000
Preferred Units [Member]
Schedule of Capitalization, Equity [Line Items]
Conversion of stock, units converted								12,771
Common Units [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold										450
Conversion of stock, units converted								3,490,884
Stock Purchase Agreement [Member]
Schedule of Capitalization, Equity [Line Items]
Common stock, par value	$ 0.00001
Number of additional shares issued and sold	70,000
Shares issued, price per share	$ 11.00
Proceeds from issue of common stock	$ 770,000,000
Lock-up period of shares	6 months
Transaction closing date	Nov. 02, 2017
Director [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold			130,590
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
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		1,600,000
Net proceeds from issuance of common stock, after deducting offering expenses		$ 40,700,000
Conversion of preferred stock to common stock, shares		2,061,773
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
Sun Pharma Offering [Member]
Schedule of Capitalization, Equity [Line Items]
Conversion of preferred stock to common stock, shares		2,061,773
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
Shares issued, price per share				$ 7.66
Aggregate proceeds from issuance of preferred stock				$ 7,000,000
Preferred stock, convertible beneficial conversion feature				$ 3,200,000

Capitalization - Schedule of Mandatory Conversion of Notes into Preferred Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Aug. 08, 2017	Dec. 31, 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)
Series A 1 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	844,362
Fair Value Preferred Stock	$ 6,466
Series A 2 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	123,691
Fair Value Preferred Stock	$ 947
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 [Member] \| Series A 1 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	607,743
Fair Value Preferred Stock	$ 4,654
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] \| Note Purchase Agreement - Related Parties [Member] \| Series A 1 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	236,619
Fair Value Preferred Stock	$ 1,812
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] \| Second Note Purchase Agreement - Related Parties [Member] \| Series A 2 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	123,691
Fair Value Preferred Stock	$ 947
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)
Convertible Promissory Notes [Member] \| Agreements - Related Parties [Member] \| Series A 1 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	236,619
Fair Value Preferred Stock	$ 1,812
Convertible Promissory Notes [Member] \| Agreements - Related Parties [Member] \| Series A 2 Preferred Stock [Member]
Debt Conversion [Line Items]
Shares of Preferred Stock	123,691
Fair Value Preferred Stock	$ 947

Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2017 shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) Employee 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	142,105
Stock options granted		71,649	142,105
Stock-based compensation expense \| $		$ 246	$ 33
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $		$ 151	25
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 \| $		$ 130	$ 3
Number of employees \| Employee			0
Unrecognized stock-based compensation expense \| $		$ 623
Estimated weighted average period		3 years
Non-Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted under the plan		0
Unrecognized stock-based compensation expense \| $		$ 93
Estimated weighted average period		2 years 10 months 24 days
Non-Employee Stock Option [Member] \| Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $		$ 116	$ 30
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
Stock option vesting period		4 years
Stock option expiration period		10 years
Number of shares granted under the plan	113,683
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
Stock option vesting period		4 years
Stock option expiration period		10 years
Options to purchase of shares of common stock	113,683
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

Stock-Based Compensation - Schedule of Company's Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares outstanding, beginning balance	142,105
Shares, granted	71,649	142,105
Shares, exercised	0	0
Shares, cancelled or forfeited	(28,422)
Shares outstanding, ending balance	185,332	142,105
Shares exercisable at December 31, 2017	43,221
Shares vested at December 31, 2017	43,221
Weighted-average exercise price outstanding, beginning balance	$ 2.46
Weighted-average exercise price, granted	6.22	$ 2.46
Weighted-average exercise price, exercised	0
Weighted-average exercise price, cancelled or forfeited	2.46
Weighted-average exercise price outstanding, ending balance	3.91	$ 2.46
Weighted-average exercise price exercisable at December 31, 2017	2.46
Weighted-average exercise price vested at December 31, 2017	$ 2.46
Weighted-average remaining contractual life (years), granted		9 years 8 months 12 days
Weighted-average remaining contractual life (years), outstanding	9 years	9 years 8 months 12 days
Weighted-average remaining contractual life (years), exercisable	8 years 8 months 12 days
Weighted-average remaining contractual life (years), vested	8 years 8 months 12 days
Aggregate intrinsic value, outstanding	$ 1,224	$ 338
Aggregate intrinsic value, exercisable	348
Aggregate intrinsic value, vested	$ 348

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Deferred tax assets	$ 0	$ 0
Deferred tax liabilities		0
Deferred tax assets, net operating Loss carryforwards	2,029,000	0
Current income tax expense (benefit)	0	0
Deferred income tax expense (benefit)	$ 0	$ 0
Statutory federal and state income tax rate	28.00%	28.00%
Cumulative changes in ownership interest rate period	3 years
Tax cuts and jobs act of 2017, net operating loss deduction limitation, percent of taxable income	80.00%
Minimum [Member]
Income Taxes [Line Items]
Cumulative changes in ownership interest of shareholders	50.00%
U.S. Federal [Member]
Income Taxes [Line Items]
NOL carryforwards	$ 7,400,000	$ 0

Related Party Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Sep. 22, 2017	Aug. 25, 2017	Aug. 08, 2017	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Related Party Transaction [Line Items]
Related party convertible promissory notes				$ 0	$ 698
Preferred units, outstanding				0	1,406
Preferred stock, shares issued						179,613
Aggregate proceeds from issuance of preferred stock				7,000	1,306
Proceeds from sale of common stock				$ 42,469	100
IPO [Member]
Related Party Transaction [Line Items]
Shares issued, price per share	$ 10.00
Number of shares issued and sold	4,554,000
IPO [Member] \| Chief Executive Officer [Member]
Related Party Transaction [Line Items]
Shares issued, price per share				$ 10
Number of shares issued and sold				100,000
IPO [Member] \| Chief Operating Officer [Member]
Related Party Transaction [Line Items]
Shares issued, price per share				$ 10
Number of shares issued and sold				100,000
Series A Preferred Stock [Member]
Related Party Transaction [Line Items]
Shares issued, price per share			$ 7.66
Series A Preferred Stock [Member] \| Sun Pharma Offering [Member]
Related Party Transaction [Line Items]
Preferred stock, shares issued			914,107
Shares issued, price per share			$ 7.66
Aggregate proceeds from issuance of preferred stock			$ 7,000
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
Proceeds from sale of common stock		$ 1,000

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 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

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Installment	Dec. 31, 2016 USD ($)
Operating Leased Assets [Line Items]
Rent expense	$ 86	$ 54
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
Clinical Supply Agreement
Operating Leased Assets [Line Items]
Estimated remaining commitment	$ 289
Project management service fee	$ 1,500	$ 11

Net Loss Per Share Attributable to Common Stockholders and Members - Schedule of Basic and Diluted Net Loss Per Share and Per Unit (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss applicable to common stockholders and members	$ (7,920)	$ (1,150)
Denominator:
Weighted-average basic and diluted common shares and common units	5,360,536	877,490
Basic and diluted net loss per common share and common unit	$ (1.48)	$ (1.31)

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Total property and equipment	$ 225	$ 15
Accumulated depreciation and amortization	(25)	(2)
Property and equipment, net	200	13
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	11	8
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 214	$ 7

Balance Sheet Components - Schedule of Accrued Expenses And Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance Sheet Components [Abstract]
Accrued pre-clinical expenses	$ 257
Accrued Professional fees	77
Accrued payroll and benefits	10
Accrued taxes	103	$ 1
Total	$ 447	$ 1

Income Taxes - Significant Components of Deferred Tax Assets (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Deferred tax assets, net operating Loss carryforwards	$ 2,029,000	$ 0
Non-qualified option	29,000
Depreciation	(31,000)
Accrued expenses	137,000
Total deferred tax assets	2,164,000
Valuation allowance	(2,164,000)
Net deferred tax assets	$ 0	$ 0