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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	Apr. 30, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	KRYS
Entity Registrant Name	Krystal Biotech, Inc.
Entity Central Index Key	0001711279
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		14,443,569
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 98,013	$ 103,670
Short-term investments	8,617	8,091
Prepaid and other current assets	1,264	889
Total current assets	107,894	112,650
Property and equipment, net	4,354	3,014
Right-of-use asset	3,001
Other noncurrent assets	455	452
Total assets	115,704	116,116
Current liabilities
Accounts payable	1,126	888
Current portion of lease liability	418
Accrued expenses and other current liabilities	1,698	1,708
Total current liabilities	3,242	2,596
Lease liability	2,976
Other noncurrent liabilities		294
Total liabilities	6,218	2,890
Commitments and contingencies (Note 5)
Stockholders' equity
Preferred stock; $0.00001 par value; 20,000,000 shares authorized at March 31, 2019 (unaudited) and December 31, 2018; 2,061,773 shares issued, and no shares outstanding at March 31, 2019 (unaudited) and December 31, 2018	0	0
Common stock; $0.00001 par value; 80,000,000 shares authorized at March 31, 2019 (unaudited) and December 31, 2018; 14,443,569 and 14,428,916 shares issued and outstanding at March 31, 2019 (unaudited) and December 31, 2018, respectively	0	0
Additional paid-in capital	133,540	133,183
Accumulated other comprehensive income	16	2
Accumulated deficit	(24,070)	(19,959)
Total stockholders' equity	109,486	113,226
Total liabilities and stockholders' equity	$ 115,704	$ 116,116

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Expenses
Research and development	$ 3,167	$ 1,520
General and administrative	1,527	757
Total operating expenses	4,694	2,277
Loss from operations	(4,694)	(2,277)
Other Expense
Interest and other income, net	583	127
Total interest and other income, net	583	127
Net loss	(4,111)	(2,150)
Unrealized gain on available-for-sale securities	14
Comprehensive loss	$ (4,097)	$ (2,150)
Net loss attributable to common stockholders per share: Basic and diluted	$ (0.29)	$ (0.21)
Weighted-average common shares outstanding: Basic and diluted	14,417,649	10,307,379

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2017	$ 49,474		$ 58,544		$ (9,070)
Begining Balance, shares at Dec. 31, 2017		10,307,247
Issuance of common stock	10		10
Issuance of common stock, shares		2,368
Stock-based compensation expense	65		65
Net loss	(2,150)				(2,150)
Ending balance at Mar. 31, 2018	47,399		58,619		(11,220)
Ending Balance, shares at Mar. 31, 2018		10,309,615
Beginning balance at Dec. 31, 2018	113,226		133,183	$ 2	(19,959)
Begining Balance, shares at Dec. 31, 2018		14,428,916
Issuance of common stock	44		44
Issuance of common stock, shares		14,653
Stock-based compensation expense	313		313
Unrealized gain on investments	14			14
Net loss	(4,111)				(4,111)
Ending balance at Mar. 31, 2019	$ 109,486		$ 133,540	$ 16	$ (24,070)
Ending Balance, shares at Mar. 31, 2019		14,443,569

- Definition

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

+ References + Details

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Activities
Net loss	$ (4,111)	$ (2,150)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	132	18
Stock-based compensation expense	313	65
Decrease in
Prepaids and other current assets	(352)	(118)
Accounts payable	583	(104)
Accrued expenses and other current liabilities	153	(80)
Amortization of right-of-use asset	67
Net cash used in operating activities	(3,215)	(2,369)
Investing Activities
Purchases of property and equipment	(1,707)
Purchases of short-term investments	(512)
Purchases of other noncurrent assets	(263)
Net cash used in investing activities	(2,482)
Financing Activities
Issuance of common stock, net	40	6
Net cash provided by financing activities	40	6
Net decrease in cash and cash equivalents	(5,657)	(2,363)
Cash and cash equivalents at beginning of period	103,670	49,591
Cash and cash equivalents at end of period	98,013	47,228
Supplemental Disclosures of Non-Cash Investing and Financing Activities
Unpaid purchase of property and equipment	375
Unpaid deferred offering costs	155	$ 1
Initial recognition of right-of-use assets	$ 3,394

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. In the opinion of management, the condensed consolidated financial statements reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s condensed consolidated financial information. The results of operations for the three-month period ended March 31, 2019 are not necessarily indicative of the results to be expected for the full year or any other future period. The condensed consolidated balance sheet as of December 31, 2018 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements.

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 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.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Financial instruments that potentially subject the Company to credit risk consist of cash, cash equivalents and short-term investments. The Company’s policy is to invest its cash and cash equivalents in money market funds and various bank deposit accounts. 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 Equivalents and Short-Term Investments

Cash and cash equivalents consist of money market funds and bank deposits. Cash equivalents are defined as short-term, highly liquid investments with original maturities of 90 days or less at the date of purchase.

Investments with maturities of greater than 90 days but less than one year are classified as short-term investments on the condensed consolidated balance sheets and consist of U.S. Treasury bills and certificates of deposit. Accrued interest on U.S. Treasury bills and certificates of deposit are also classified as short-term investments.

As our entire investment portfolio is considered available for use in current operations, we classify all investments as available-for-sale and as current assets. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive gain or loss, which is a separate component of stockholders’ equity in the condensed consolidated balance sheets.

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 periods presented. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of financial instruments between levels during the periods presented.

The carrying amounts of financial instruments consisting of cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities included in the Company’s financial statements, are reasonable estimates of fair value, primarily due to their short maturities.

Our available-for-sale short-term investments, which consist of US Treasury bills and certificates of deposit, are considered to be level 2. The fair value of Level 2 financial assets is determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis.

Property and Equipment, net

Property and equipment, net, 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

Furniture and fixtures

Leasehold improvements

3-7 years

3 years

remaining life of lease

Construction-in-progress is not depreciated until the asset is placed in service.

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 March 31, 2019.

Leases

We have entered into a lease agreement for our laboratory and office space. As described below under "Recent Accounting Standards,” we adopted ASU 2016-02 – Leases (Topic 842) (“ASU 2016-02”) as of January 1, 2019. Pursuant to ASU 2016-02, all of our leases outstanding on January 1, 2019 continued to be classified as operating leases. With the adoption of ASU 2016-02, we recorded an operating lease right-of-use asset and an operating lease liability on our balance sheet. Right-of-use lease assets represent our right to use the underlying asset during the lease term and the lease obligation represents our commitment to make lease payments arising from the lease. Right-of-use lease assets and obligations were recognized based on the present value of remaining lease payments over the lease term. As the Company’s leases do not provide an implicit rate, we have used an estimated incremental borrowing rate based on the information available at our adoption date in determining the present value of lease payments. Operating lease expense is recognized on a straight-line basis over the lease term. Variable lease costs such as common area costs and other operating costs are expensed as incurred. For all lease agreements we combine lease and non-lease components. Leases with an initial term of 12 months or less are not recorded on the balance sheet.

Prior to our adoption of ASU 2016-02, when our lease agreements contained tenant improvement allowances and rent escalation clauses, we recorded a deferred rent asset or liability equal to the difference between the rent expense and the future minimum lease payments due. The lease expense related to operating leases was recognized on a straight-line basis in the statements of operations over the term of each lease. In cases where the lessor granted us leasehold improvement allowances that reduced our lease expense, we capitalized the improvements as incurred and recognized deferred rent, which was amortized over the shorter of the lease term or the expected useful life of the improvements.

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. Beginning in the first quarter of 2019, the Company adopted ASU 2018-07 - Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which no longer required non-employee stock options to be periodically revalued. The adoption of this amended guidance did not have a material effect on our condensed consolidated financial statements. Prior to the first quarter of 2019, share-based payments issued to non-employees were recorded at their fair values and were periodically revalued as the equity instruments vest and were recognized as expense over the related service period in accordance with the provisions of ASC 718 and ASC Topic 505, Equity, and were expensed ratably over the vesting term.

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. Beginning in the first quarter of 2019, the expected term of non-employee stock options also used the “simplified” method. Prior to the first quarter of 2019, the expected term for non-employee awards was 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 to revise those estimates in subsequent periods if actual forfeitures differ from its estimates. Beginning in the first quarter of 2019, the Company used historical data to estimate forfeitures and recorded stock-based compensation expense only for those awards that were expected to vest. Prior to the first quarter of 2019, the forfeiture rate was estimated to be zero. 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.

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 income or loss are reported, net of their related tax effect, to arrive at a comprehensive loss.

Recent Accounting Pronouncements

In August 2018, the SEC issued a final rule to simplify certain disclosure requirements. In addition, the amendments expanded the disclosure requirements on the analysis of stockholders’ equity for interim financial statements. In August and September 2018, further amendments were issued to provide implementation guidance on adoption of the SEC rule and transition guidance for the new interim stockholders’ equity disclosure. We adopted this amended guidance in the first quarter of 2019. The adoption of this amended guidance resulted in us disclosing the Condensed Consolidated Statements of Stockholders’ Equity for the three months ending March 31, 2018 and 2019.

In August 2018, the FASB issued ASU 2018-13 - Fair Value Measurement (Topic 820) (“ASU 2018-13”) which removes, modifies and adds disclosure requirements on fair value measurements. ASU 2018-13 removes disclosure requirements for transfers between Level 1 and Level 2 measurements and valuation processes for Level 3 measurements but adds new disclosure requirements including changes in unrealized gains/losses in other comprehensive income related to recurring Level 3 measurements. The amended guidance is effective for us commencing in the first quarter of 2020. Certain aspects may be applied prospectively while other aspects may be applied retrospectively upon the effective date. Early adoption is permitted. We are in the process of evaluating the effect of this guidance on our consolidated financial statements and related disclosures.

In June 2018, the FASB issued ASU 2018-07 - Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting which simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The new guidance expands the scope of ASC 718 to include share-based payments granted to nonemployees in exchange for goods or services used or consumed in an entity’s own operations. The amended guidance is effective for us commencing in the first quarter of 2019. The adoption of this amended guidance did not have a material effect on our condensed consolidated financial statements.

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 with terms longer than 12 months will result in the lessee recognizing a right-of-use asset and a 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. In July 2018, further amendments were issued to clarify how to apply certain aspects of the amended lease guidance and to address certain implementation issues. ASU 2016-02 is effective for the Company beginning in the first quarter of 2019. The Company generally does not finance purchases of equipment but does lease office and lab facilities. The adoption of this amended guidance resulted in $3.0 million of right-of-use asset and $3.4 million of lease liability being recognized on the condensed consolidated balance sheet as of March 31, 2019.

Balance Sheet Components

3 Months Ended

Mar. 31, 2019

Balance Sheet Components [Abstract]

Balance Sheet Components

4.	Balance Sheet Components

Property and Equipment, Net

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

	March 31, 2019			December 31, 2018
	(Unaudited)
Construction-in-progress		309			2,259
Leasehold improvements		2,171			3
Furniture & fixtures		99			99
Computer equipment and software		48			40
Laboratory equipment		2,025			779
Total property and equipment		4,652			3,180
Accumulated depreciation and amortization		(298	)		(166	)
Property and equipment, net	$	4,354		$	3,014

Depreciation expense was $132 thousand and $18 thousand for the three months ended March 31, 2019 and 2018, respectively.

Accrued Expenses and Other Current Liabilities

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

	March 31, 2019		December 31, 2018
	(Unaudited)
Accrued pre-clinical expenses	$	675	$	537
Accrued professional fees		159		41
Accrued payroll and benefits		256		348
Accrued taxes		50		154
Accrued construction in progress		330		589
Other current liabilities		646		39
Total	$	2,116	$	1,708

Stock-Based Compensation

3 Months Ended

Mar. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

7.	Stock-Based Compensation

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 on Form S-1 relating to our IPO. 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 67,500 and 55,000 stock options to employees and directors of the Company during the three months ended March 31, 2019 and 2018, respectively. Options granted to employees vest ratably over a four-year period and options granted to directors of the company vest ratably between one and four-year periods. Options have a life of ten years. Commencing in the first quarter of 2019, the accounting treatment for stock options granted to non-employees was aligned with the accounting for employee stock options upon the adoption of ASU 2018-07 as described in Note 2 “Summary of Significant Accounting Policies”. Prior to the first quarter of 2019, stock options granted to non-employees were accounted for using the fair value method of accounting, and are periodically revalued as the options vest, and recognized as expense over the related service period.

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

						Weighted-
				Weighted-		average		Aggregate
	Stock			average		Remaining		Intrinsic
	Options			Exercise		Contractual		Value
	Outstanding			Price		Life (Years)		(In thousands) ⁽¹⁾
Balance at December 31, 2018		357,089		$	8.73		8.8	$	4,302
Granted		67,500		$	23.87
Exercised		(14,653	)	$	2.75
Cancelled or forfeited		(9,000	)	$	18.71
Balance at March 31, 2019		400,936		$	11.28		8.8	$	8,670
Exercisable at March 31, 2019		93,468		$	5.82		8.2	$	2,531
Vested at March 31, 2019		112,364		$	5.30		8.2	$	3,102

(1)

Aggregate intrinsic value represents the difference between the closing stock price of our common stock on March 31, 2019 and the exercise price of outstanding in-the-money options.

Options for 14,653 shares of our common stock with an intrinsic value of $442 thousand were exercised during the three months ended March 31, 2019.

The Company has recorded aggregate stock-based compensation expense related to the issuance of stock option awards to employees and non-employees in the condensed consolidated statements of operations for the three months ended March 31, 2019 and 2018 as follows (in thousands):

	Three Months Ended March 31,
	2019		2018
Research and development	$	117	$	46
General and administrative		87		19
Total stock-based compensation	$	204	$	65

Stock Options Granted to Employees. The Company recorded stock-based compensation expense related to employee’s and board member’s stock options of $185 thousand and $61 thousand for the three months ended March 31, 2019 and 2018, respectively. 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 months ended March 31, 2019 and 2018:

	Three Months Ended March 31,
	2019			2018
Expected stock price volatility		71	%		80	%
Expected term of the award (years)		6.25			6.25
Risk-free interest rate		2.46	%		2.71	%
Forfeiture Rate		10.00	%		0.00	%
Expected dividend yield		0	%		0	%

The weighted-average grant-date fair value per share of options granted to employees during the three months ended March 31, 2019 was $15.51.

There was $1.5 million of unrecognized stock-based compensation expense related to employees’ awards that is expected to be recognized over a weighted-average period of 2.88 years as of March 31, 2019.

Stock Options Granted to Non-Employees. The Company recorded stock-based compensation expense related to non-employees’ stock options of $19 thousand and $4 thousand for the three months ended March 31, 2019 ad 2018, respectively.

Restricted Stock Awards. The Company granted 26,213 and 16,213 restricted stock awards (“RSA”s) on June 1, 2018 to our Chief Executive Officer and Chief Operating Officer, respectively. The RSAs vest ratably over a one-year period. 31,818 shares of RSAs had vested as of March 31, 2019. The RSAs, including the unvested portion, are considered issued and outstanding as of March 31, 2019. The fair value of each restricted stock was $10.30 reflecting the closing price of our common stock on the grant date. The Company recorded stock-based compensation expense related to RSAs of $109 thousand and $0 for the three months ended March 31, 2019 and 2018, respectively within general and administrative expenses in the accompanying condensed consolidated statements of operations. As of March 31, 2019, there was $73 thousand of unrecognized stock-based compensation expense related to RSAs that is expected to be recognized over a weighted-average period of 2 months.

Stock options and restricted stock awards available for grant were 623,074 at March 31, 2019.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2019

Accounting Policies [Abstract]

Unaudited Condensed Consolidated Financial Information

Error extracting Word content

Basis of Presentation

Use of Estimates

Segment and Geographical Information

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash, Cash Equivalents and Short-Term Investments

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

Furniture and fixtures

Leasehold improvements

3-7 years

3 years

remaining life of lease

Construction-in-progress is not depreciated until the asset is placed in service.

Impairment of Long-Lived Assets

Leases

Research and Development Expenses

Stock-Based Compensation Expense

Comprehensive Loss

Recent Accounting Pronouncements

Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2019

Balance Sheet Components [Abstract]

Schedule of Property and Equipment, Net

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

	March 31, 2019			December 31, 2018
	(Unaudited)
Construction-in-progress		309			2,259
Leasehold improvements		2,171			3
Furniture & fixtures		99			99
Computer equipment and software		48			40
Laboratory equipment		2,025			779
Total property and equipment		4,652			3,180
Accumulated depreciation and amortization		(298	)		(166	)
Property and equipment, net	$	4,354		$	3,014

Schedule of Accrued Expenses And Other Current Liabilities

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

	March 31, 2019		December 31, 2018
	(Unaudited)
Accrued pre-clinical expenses	$	675	$	537
Accrued professional fees		159		41
Accrued payroll and benefits		256		348
Accrued taxes		50		154
Accrued construction in progress		330		589
Other current liabilities		646		39
Total	$	2,116	$	1,708

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Schedule of Company's Stock Option Activity

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

						Weighted-
				Weighted-		average		Aggregate
	Stock			average		Remaining		Intrinsic
	Options			Exercise		Contractual		Value
	Outstanding			Price		Life (Years)		(In thousands) ⁽¹⁾
Balance at December 31, 2018		357,089		$	8.73		8.8	$	4,302
Granted		67,500		$	23.87
Exercised		(14,653	)	$	2.75
Cancelled or forfeited		(9,000	)	$	18.71
Balance at March 31, 2019		400,936		$	11.28		8.8	$	8,670
Exercisable at March 31, 2019		93,468		$	5.82		8.2	$	2,531
Vested at March 31, 2019		112,364		$	5.30		8.2	$	3,102

(1)

Aggregate intrinsic value represents the difference between the closing stock price of our common stock on March 31, 2019 and the exercise price of outstanding in-the-money options.

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

	Three Months Ended March 31,
	2019		2018
Research and development	$	117	$	46
General and administrative		87		19
Total stock-based compensation	$	204	$	65

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 months ended March 31, 2019 and 2018:

	Three Months Ended March 31,
	2019			2018
Expected stock price volatility		71	%		80	%
Expected term of the award (years)		6.25			6.25
Risk-free interest rate		2.46	%		2.71	%
Forfeiture Rate		10.00	%		0.00	%
Expected dividend yield		0	%		0	%

Commitments and Contingencies - Schedule of Future Minimum Operating Lease Payments (Detail) $ in Thousands	Mar. 31, 2019 USD ($)
Operating Leased Assets [Line Items]
Present value of lease liability	$ 3,400
Current portion of lease liability	418
Long-term portion of lease liability	2,976
Fourth Amendment to 2016 Lease Agreement [Member]
Operating Leased Assets [Line Items]
2019 (remaining nine months)	321
2020	515
2021	592
2022	604
2023	616
Thereafter	2,033
Future minimum operating lease payments	4,681
Less: Interest	1,287
Present value of lease liability	3,394
Current portion of lease liability	418
Long-term portion of lease liability	$ 2,976

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Sep. 05, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted	67,500	55,000
Stock option expiration period	10 years
Options exercised	14,653
Intrinsic value of options exercised	$ 442
Stock-based compensation expense	$ 204	$ 65
Stock options and restricted stock awards available for grant	623,074
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 117	46
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	4 years
Weighted-average grant-date fair value per share of options granted	$ 15.51
Unrecognized stock-based compensation expense	$ 1,500
Estimated weighted average period	2 years 10 months 17 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	$ 19	4
Non-Employee Stock Option [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	1 year
Non-Employee Stock Option [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	4 years
Employee's and Board Member's Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 185	61
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	1 year
Stock-based compensation expense	$ 109	$ 0
Weighted-average grant-date fair value per share of options granted	$ 10.30
Unrecognized stock-based compensation expense	$ 73
Estimated weighted average period	2 months
Number of restricted stock award vested		31,818
Restricted Stock [Member] \| Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock award granted	26,213	26,213
Restricted Stock [Member] \| Chief Operating Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock award granted	16,213	16,213
2017 IPO Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorization to issue number of common stock			900,000

Stock-Based Compensation - Schedule of Company's Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Options Outstanding, Beginning balance	357,089
Stock Options Outstanding, Granted	67,500	55,000
Stock Options Outstanding, Exercised	(14,653)
Stock Options Outstanding, Cancelled or forfetied	(9,000)
Stock Options Outstanding, Ending balance	400,936		357,089
Stock Options Outstanding, Exercisable at March 31, 2019	93,468
Stock Options Outstanding, Vested at March 31, 2019	112,364
Weighted-average Exercise Price, Beginning balance	$ 8.73
Weighted-average Exercise Price, Granted	23.87
Weighted-average Exercise Price, Exercised	2.75
Weighted-average Exercise Price, Cancelled or forfeited	18.71
Weighted-average Exercise Price, Ending balance	11.28		$ 8.73
Weighted-average Exercise Price, Exercisable at March 31, 2019	5.82
Weighted-average Exercise Price, Exercisable at March 31, 2019	$ 5.30
Weighted-average Remaining Contractual Life (Years)	8 years 9 months 18 days		8 years 9 months 18 days
Weighted-average Remaining Contractual Life (Years), Exercisable	8 years 2 months 12 days
Weighted-average Remaining Contractual Life (Years), Vested	8 years 2 months 12 days
Aggregate intrinsic value, outstanding	$ 8,670		$ 4,302
Aggregate Intrinsic Value, Exercisable	2,531
Aggregate Intrinsic Value, Vested	$ 3,102

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.00001	$ 0.00001
Convertible preferred stock, shares authorized	20,000,000	20,000,000
Convertible preferred stock, shares issued	2,061,773	2,061,773
Convertible preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	80,000,000	80,000,000
Common stock, shares issued	14,443,569	14,428,916
Common stock, shares outstanding	14,443,569	14,428,916

Organization - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (24,070)	$ (19,959)
Cash, cash equivalents and short-term investments	$ 106,600

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) Segment	Dec. 31, 2018
Accounting Policies [Abstract]
Number of operating segment \| Segment	1
Recognized impairment losses for long lived assets	$ 0
Estimated forfeiture rate		0.00%
Right-of-use asset	3,001,000
Operating lease, liability	$ 3,400,000

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Assets (Detail)	3 Months Ended
	Mar. 31, 2019
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	3 years
Laboratory Equipment [Member] \| Minimum [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	3 years
Laboratory Equipment [Member] \| Maximum [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	7 years
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	3 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Estimated useful lives of assets	remaining life of lease

Net Loss Per Share Attributable to Common Stockholders - Additional Information (Detail) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Stock conversion rate			100.00%
Common share equivalents outstanding, excluded from the calculation of diluted net loss per share attributable to common stock holders	443,362	233,464

Net Loss Per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss Per Share and Per Unit (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net loss applicable to common stockholders and members	$ (4,111)	$ (2,150)
Denominator:
Weighted-average basic and diluted common shares and common units	14,417,649	10,307,379
Basic and diluted net loss per common share and common unit	$ (0.29)	$ (0.21)

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 4,652	$ 3,180
Accumulated depreciation and amortization	(298)	(166)
Property and equipment, net	4,354	3,014
Construction-in-progress [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	309	2,259
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	2,171	3
Furniture & Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	99	99
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	48	40
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 2,025	$ 779

Balance Sheet Components - Schedule of Accrued Expenses And Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Components [Abstract]
Accrued pre-clinical expenses	$ 675	$ 537
Accrued professional fees	159	41
Accrued payroll and benefits	256	348
Accrued taxes	50	154
Accrued construction in progress	330	589
Other current liabilities	646	39
Total	$ 2,116	$ 1,708

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) ft²	Mar. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Right-of-use asset	$ 3,001
Operating lease, liability	3,400
Rent expense	$ 125	$ 31
2016 Lease Agreement [Member]
Operating Leased Assets [Line Items]
Lease expiration date	Feb. 28, 2027
Additional area of real estate property leased \| ft²	31,000
Clinical Supply Agreement [Member]
Operating Leased Assets [Line Items]
Estimated remaining commitment	$ 2,200
Project management service fee	$ 803	$ 801

Capitalization - Additional Information (Detail) - USD ($)			3 Months Ended
	Mar. 12, 2019	Nov. 01, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Schedule of Capitalization, Equity [Line Items]
Common stock, par value			$ 0.00001		$ 0.00001
Proceeds from issue of common stock			$ 40,000	$ 6,000
Common stock, shares outstanding			14,443,569		14,428,916
Preferred stock, shares outstanding			0		0
ATM Facilty [Member]
Schedule of Capitalization, Equity [Line Items]
Agreed sale price of shares	$ 50,000,000
Compensation entitled as percentage of gross proceeds of shares sold under ATM Facility	3.00%
Stock Purchase Agreement [Member]
Schedule of Capitalization, Equity [Line Items]
Number of additional shares issued and sold		70,000
Common stock, par value		$ 0.00001
Shares issued, price per share		$ 11.00
Proceeds from issue of common stock		$ 770,000
Transaction closing date		Nov. 02, 2017