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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Jul. 31, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	CRNX
Entity Registrant Name	Crinetics Pharmaceuticals, Inc.
Entity Central Index Key	0001658247
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38583
Entity Tax Identification Number	263744114
Entity Address, Address Line One	10222 Barnes Canyon Road
Entity Address, Address Line Two	Bldg. #2
Entity Address, City or Town	San Diego
Entity Address, State or Province	California
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	450-6464
Entity Common Stock, Shares Outstanding		24,199,972

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 59,716	$ 44,973
Investment securities	85,258	118,902
Prepaid expenses and other current assets	2,784	2,808
Total current assets	147,758	166,683
Property and equipment, net	4,264	4,232
Operating lease right-of-use asset	2,627
Restricted cash	500	500
Total assets	155,149	171,415
Current liabilities:
Accounts payable	2,705	1,456
Accrued expenses and other current liabilities	3,243	4,190
Accrued compensation and benefits	1,802	2,279
Total current liabilities	7,750	7,925
Non-current operating lease liability	5,226
Deferred rent		3,063
Unvested stock liability	72	202
Total liabilities	13,048	11,190
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.001 par, 10,000 shares authorized; no shares issued or outstanding at June 30, 2019 or at December 31, 2018
Common stock and paid-in capital, $0.001 par, 200,000 shares authorized; 24,245 and 24,195 shares issued and outstanding at June 30, 2019; 24,188 and 24,061 shares issued and outstanding at December 31, 2018	206,690	203,544
Accumulated other comprehensive income	234	61
Accumulated deficit	(64,823)	(43,380)
Total stockholders’ equity	142,101	160,225
Total liabilities and stockholders’ equity	$ 155,149	$ 171,415

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock and paid-in capital, par value	$ 0.001	$ 0.001
Common stock and paid-in capital, shares authorized	200,000,000	200,000,000
Common stock and paid-in capital, shares issued	24,245,000	24,188,000
Common stock and paid-in capital, shares outstanding	24,195,000	24,061,000

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Grant revenues		$ 657	$ 367	$ 1,099
Type of Revenue Extensible List	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses:
Research and development	$ 10,285	$ 5,222	$ 17,540	$ 9,942
General and administrative	3,060	1,118	6,216	2,366
Total operating expenses	13,345	6,340	23,756	12,308
Loss from operations	(13,345)	(5,683)	(23,389)	(11,209)
Other income (expense):
Interest income	960	151	1,970	215
Other income (expense)	(42)	(36)	(24)	(38)
Total other income (expense), net	918	115	1,946	177
Net loss	(12,427)	(5,568)	(21,443)	(11,032)
Other comprehensive income (loss):
Unrealized gain on investment securities	89		173
Comprehensive loss	$ (12,338)	$ (5,568)	$ (21,270)	$ (11,032)
Net loss per share:
Net loss per share – basic and diluted	$ (0.51)	$ (2.41)	$ (0.89)	$ (5.28)
Weighted-average shares outstanding – basic and diluted	24,161	2,307	24,128	2,089

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Common stock and Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Temporary equity, Beginning Balance at Dec. 31, 2017		$ 29,700
Temporary equity, Beginning Balance, Shares at Dec. 31, 2017		28,763,000
Beginning Balance at Dec. 31, 2017	$ (15,022)			$ 1,243		$ (16,265)
Beginning Balance, Shares at Dec. 31, 2017			1,550,000
Temporary equity, Issuance of convertible preferred stock		$ 63,275
Temporary equity, Issuance of convertible preferred stock, shares		19,641,000
Vesting of stock subject to repurchase	8			8
Vesting of stock subject to repurchase, shares			529,000
Exercise of stock options	171			171
Exercise of stock options, shares			265,000
Stock-based compensation	698			698
Net loss	(11,032)					(11,032)
Ending Balance at Jun. 30, 2018	(25,177)			2,120		(27,297)
Ending Balance, Shares at Jun. 30, 2018			2,344,000
Temporary equity, Ending Balance at Jun. 30, 2018		$ 92,975
Temporary equity, Ending Balance, Shares at Jun. 30, 2018		48,404,000
Temporary equity, Beginning Balance at Mar. 31, 2018		$ 92,975
Temporary equity, Beginning Balance, Shares at Mar. 31, 2018		48,404,000
Beginning Balance at Mar. 31, 2018	(19,976)			1,753		(21,729)
Beginning Balance, Shares at Mar. 31, 2018			2,191,000
Vesting of stock subject to repurchase	5			5
Vesting of stock subject to repurchase, shares			3,000
Exercise of stock options	91			91
Exercise of stock options, shares			150,000
Stock-based compensation	271			271
Net loss	(5,568)					(5,568)
Ending Balance at Jun. 30, 2018	(25,177)			2,120		(27,297)
Ending Balance, Shares at Jun. 30, 2018			2,344,000
Temporary equity, Ending Balance at Jun. 30, 2018		$ 92,975
Temporary equity, Ending Balance, Shares at Jun. 30, 2018		48,404,000
Beginning Balance at Dec. 31, 2018	160,225			203,544	$ 61	(43,380)
Beginning Balance, Shares at Dec. 31, 2018			24,061,000
Vesting of stock subject to repurchase	71			71
Vesting of stock subject to repurchase, shares			46,000
Exercise of stock options	$ 87			87
Exercise of stock options, shares	63,014		63,000
Issuance of stock under Stock Purchase Plan	$ 379			379
Issuance of stock under Stock Purchase Plan, shares			25,000
Stock-based compensation	2,609			2,609
Comprehensive income	173				173
Net loss	(21,443)					(21,443)
Ending Balance at Jun. 30, 2019	142,101			206,690	234	(64,823)
Ending Balance, Shares at Jun. 30, 2019			24,195,000
Beginning Balance at Mar. 31, 2019	152,394			204,645	145	(52,396)
Beginning Balance, Shares at Mar. 31, 2019			24,115,000
Vesting of stock subject to repurchase	18			18	0	0
Vesting of stock subject to repurchase, shares			13,000
Exercise of stock options	67			67	0	0
Exercise of stock options, shares			42,000
Issuance of stock under Stock Purchase Plan	379			379	0	0
Issuance of stock under Stock Purchase Plan, shares			25,000
Stock-based compensation	1,581		$ 0	1,581	0	0
Comprehensive income	89		0	0	89	0
Net loss	(12,427)		$ 0	0	0	(12,427)
Ending Balance at Jun. 30, 2019	$ 142,101			$ 206,690	$ 234	$ (64,823)
Ending Balance, Shares at Jun. 30, 2019			24,195,000

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (21,443)	$ (11,032)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,609	698
Depreciation and amortization	430	124
Noncash lease expense	109
Accretion of investment securities and purchase discounts, net of amortization of purchase premiums	(689)
Other	2	76
Increase (decrease) in cash resulting from changes in:
Prepaid expenses and other current assets	24	(1,275)
Accounts payable and accrued expenses	(92)	3,652
Operating lease liability	(277)
Net cash used in operating activities	(19,327)	(7,757)
Cash flows from investing activities:
Purchases of investment securities	(52,664)
Maturities of investment securities	87,170
Purchases of property and equipment	(464)	(526)
Net cash provided by (used in) investing activities	34,042	(526)
Financing activities:
Proceeds from issuance of convertible preferred stock, net		63,266
Proceeds from exercise of stock options	87	393
Repurchase of unvested shares	(59)
Payment of initial public offering costs		(660)
Net cash provided by financing activities	28	62,999
Net change in cash, cash equivalents and restricted cash	14,743	54,716
Cash, cash equivalents and restricted cash at beginning of period	45,473	14,192
Cash, cash equivalents and restricted cash at end of period	60,216	68,908
Noncash investing and financing activities:
Purchase of shares pursuant to Employee Stock Purchase Plan	379
Change in unvested stock liability	$ (71)	(7)
Amounts accrued for purchases of property and equipment		52
Tenant improvement allowance		954
Accrued but unpaid preferred stock issuance and initial public offering costs		$ 1,046

Organization and Basis of Presentation

6 Months Ended

Jun. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Basis of Presentation

1. ORGANIZATION AND BASIS OF PRESENTATION

Description of Business

Crinetics Pharmaceuticals, Inc. (the “Company”) is a clinical stage pharmaceutical company incorporated in Delaware on November 18, 2008 and based in San Diego, California. The Company is focused on the discovery, development and commercialization of novel therapeutics for rare endocrine diseases and endocrine-related tumors. In January 2017, the Company established a wholly owned Australian subsidiary, Crinetics Australia Pty Ltd (“CAPL”), in order to conduct various preclinical and clinical activities for its development candidates.

On July 6, 2018, the Company effected a 1-for-3.29 reverse stock split of its common stock. The par value and the authorized shares of the common stock were not adjusted as a result of the reverse stock split. The reverse stock split resulted in an adjustment to the conversion prices of the Company’s Series A and B preferred stock to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying condensed consolidated financial statements and notes to the condensed consolidated financial statements give retroactive effect to the reverse stock split for all periods presented.

Unaudited Interim Financial Information

The accompanying interim condensed consolidated balance sheet as of June 30, 2019, the condensed consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2019 and 2018, the condensed consolidated statements of convertible preferred stock and stockholders’ equity (deficit) for the three and six months ended June 30, 2019 and 2018, and the condensed consolidated statements of cash flows for the six months ended June 30, 2019 and 2018, and the related disclosures are unaudited. In management’s opinion, the unaudited interim financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of June 30, 2019 and the results of its operations and cash flows for the six months ended June 30, 2019 and 2018 in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The results for the three and six months ended June 30, 2019 are not necessarily indicative of the results expected for the full fiscal year or any other interim period.

Principles of Consolidation and Foreign Currency Transactions

The condensed consolidated financial statements include the accounts of the Company and CAPL. All intercompany accounts and transactions have been eliminated in consolidation. The functional currency of both the Company and CAPL is the U.S. dollar. Assets and liabilities that are not denominated in the functional currency are remeasured into U.S. dollars at foreign currency exchange rates in effect at the balance sheet date except for nonmonetary assets, which are remeasured at historical foreign currency exchange rates in effect at the date of transaction. Net realized and unrealized gains and losses from foreign currency transactions and remeasurement are reported in other income (expense), in the condensed consolidated statements of operations and were not material for all periods presented.

Segment Reporting

Operating segments are identified as components of an enterprise about which discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.

Liquidity and Going Concern

From inception, the Company has devoted substantially all of its efforts to drug discovery and development and conducting preclinical studies and clinical trials. The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure.

As of June 30, 2019, the Company had $145.0 million in unrestricted cash, cash equivalents and investment securities. The Company believes it has sufficient cash to meet its funding requirements for at least the next 12 months. However, the Company has experienced net losses and negative cash flows from operating activities since its inception and has an accumulated deficit of $64.8 million as of June 30, 2019. The Company expects to continue to incur net losses for the foreseeable future and believes it will need to raise substantial additional capital to accomplish its business plan over the next several years. The Company plans to continue to fund its losses from operations and capital funding needs through a combination of equity offerings, debt financings or other sources, including potential collaborations, licenses and other similar arrangements. If the Company is not able to secure adequate additional funding, the Company may be forced to make reductions in spending, extend payment terms with suppliers, liquidate assets where possible, or suspend or curtail planned programs. Any of these actions could materially harm the Company’s business, results of operations and future prospects. There can be no assurance as to the availability or terms upon which such financing and capital might be available in the future.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Use of Estimates

The Company’s condensed consolidated financial statements are prepared in accordance with U.S. GAAP. The preparation of the Company’s condensed consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Company’s condensed consolidated financial statements and accompanying notes. The most significant estimates in the Company’s condensed consolidated financial statements relate to revenue recognition, accrued amounts receivable under the Australian research and development tax incentive program, accrued expenses and associated research and development expense, the assumptions underlying the determination of the estimated incremental borrowing rate for the determination of the operating lease right-of-use asset, and the assumptions underlying the determination of the fair value of equity awards for purposes of determining stock-based compensation. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.

Fair Value Measurements

The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or non-recurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Observable inputs such as quoted prices in active markets.

Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly.

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

The carrying amounts of the Company’s current financial assets, restricted cash and current financial liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments.

Cash, Cash Equivalents and Restricted Cash

The Company considers all highly liquid investments with maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts. Restricted cash represents cash held as collateral for the Company’s facility lease and is reported as a long-term asset in the accompanying condensed consolidated balance sheets.

Investment Securities

All investments have been classified as “available-for-sale” and are carried at fair value as determined based upon quoted market prices or pricing models for similar securities at period end. Investments with contractual maturities less than 12 months at the balance sheet date are considered short-term investments. Investments with contractual maturities beyond one year are also classified as short-term due to the Company’s ability to liquidate the investment for use in operations within the next 12 months.

Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold. The Company has not realized any significant gains or losses on sales of available-for-sale investment securities during any of the periods presented. Unrealized gains and losses that are determined to be temporary in nature are reported as a component of accumulated other comprehensive income (loss). A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the establishment of a new cost basis for the security. Interest income is recognized when earned and includes the amortization of purchase premiums and accretion of purchase discounts.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash balances due to the financial position of the depository institution in which those deposits are held. Additionally, the Company has established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity.

Leases

The Company determines if an arrangement is a lease at the inception of the arrangement. Leases with a term longer than 12 months that are determined to be operating leases are included in operating lease assets, accrued expenses and other current liabilities and noncurrent operating lease liabilities in the condensed consolidated balance sheets based on the present value of the minimum lease payments called for under the arrangement. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.

Grant Revenue Recognition

The Company’s grant revenues are derived from Small Business Innovation Research (“SBIR”) grants from the National Institutes of Health. The Company recognizes SBIR grant revenue as reimbursable grant costs are incurred. The costs associated with these reimbursements are reflected as a component of research and development expense in the accompanying condensed consolidated statements of operations. Earnings in excess of billings are included as a component of prepaid expenses and other current assets.

Research and Development Expenses

Research and development (“R&D”) expenses consist primarily of salaries, payroll taxes, employee benefits and stock-based compensation charges for those individuals involved in R&D efforts, as well as consulting expenses, third-party R&D expenses, laboratory supplies, clinical materials and overhead, including facilities and depreciation costs, offset by the Australian Tax Incentive discussed below. R&D expenses are charged to expense as incurred. Payments made prior to the receipt of goods or services to be used in R&D are capitalized until the goods or services are received.

Costs incurred under contracts with contract research organizations (“CROs”) that conduct and manage the Company’s clinical trials are also included in research and development expenses. The financial terms and activities of these agreements vary from contract to contract and may result in uneven expense levels. Generally, these agreements set forth activities that drive the recording of expenses such as start-up and initiation activities, enrollment and treatment of patients, or the completion of other clinical trial activities. Expenses related to clinical trials are accrued based on estimates and/or representations from service providers regarding work performed, including actual level of patient enrollment, completion of patient studies and progress of the clinical trials. Other incidental costs related to patient enrollment or treatment are accrued when reasonably certain. If the amounts that the Company is obligated to pay under its clinical trial agreements are modified (for instance, as a result of changes in the clinical trial protocol or scope of work to be performed), the Company adjusts its accruals accordingly on a prospective basis. Revisions to contractual payment obligations are charged to expense in the period in which the facts that give rise to the revision become reasonably certain.

Australian Research and Development Tax Incentive

CAPL is eligible to obtain a cash refund from the Australian Taxation Office for eligible R&D expenditures under the Australian Research and Development Tax Incentive Program (the “Australian Tax Incentive”). The Australian Tax Incentive is recognized as a reduction to R&D expense when there is reasonable assurance that the Australian Tax Incentive will be received, the relevant expenditure has been incurred, and the amount can be reliably measured. The Company recognized a reduction to R&D expense of $0.2 million and $0.6 million for the three months ended June 30, 2019 and 2018, respectively, and a reduction to R&D expense of $0.3 million and $0.9 million for the six months ended June 30, 2019 and 2018, respectively.

Stock-Based Compensation

Stock-based compensation expense represents the cost of the grant date fair value of awards over the requisite service period of the awards (usually the vesting period) on a straight-line basis. For stock awards for which vesting is subject to performance-based milestones, the expense is recorded over the remaining service period after the point when the achievement of the milestone is probable, or the performance condition has been achieved. The Company estimates the fair value of all stock option grants using the Black-Scholes option pricing model and recognizes forfeitures as they occur.

Comprehensive Loss

Comprehensive loss is comprised of the Company’s net loss for all periods presented and the unrealized gain on investment securities held as of June 30, 2019.

Net Loss Per Share

Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of convertible preferred stock, common stock subject to repurchase, and options outstanding under the Company’s stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as inclusion of the potentially dilutive securities would be antidilutive.

Recently Adopted Accounting Pronouncements

ASU 2016-02

In February 2016, the Financial Accounting Standards Board issued Accounting Standards Update (“ASU”) 2016-02, “Leases (Topic 842)” (“ASU 2016-02”) which requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. ASU 2016-02 establishes a right-of-use (ROU) model that requires a lessee to recognize a ROU asset and lease liability on the balance sheet for all leases with a term longer than 12 months. ASU 2016-02 also requires disclosures to meet the objective of enabling users of financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. On January 1, 2019, the Company adopted ASU 2016-02 using the modified retrospective transition method. Under this transition method, the Company recognized and measured leases that existed at the adoption date in the condensed consolidated balance sheet as of January 1, 2019.

ROU assets represent the right to use an underlying asset for the lease term and lease liabilities represent the obligation to make lease payments arising from the lease. Operating lease ROU assets and operating lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term, discounted at the rate implicit in the lease. If the rate implicit in the lease cannot be determined, Topic 842 requires the use of the rate of interest that a lessee would have to pay to borrow on a collateralized basis over a similar term for a similar amount to the lease payments in a similar economic environment. The operating lease ROU asset is also adjusted for any prepaid or accrued lease payments and any lease incentives received. Operating lease terms may include options to extend or terminate the lease when it is reasonably certain that these options will be exercised. Further, the Company has elected to recognize short-term lease payments on a straight-line basis over the associated lease term and variable lease payments in the period in which the obligation for those payments is incurred. Short-term and variable lease payments were not material in the first half of 2019.

In connection with the adoption of ASU 2016-02, the Company elected the package of practical expedients requiring no reassessment of whether any expired or existing contracts contain leases, the lease classification of any expired or existing leases, or initial direct costs for any existing leases. The Company also made accounting policy elections not to apply the recognition requirements under ASU 2016-02 to any short-term leases and to account for each separate lease and associated non-lease components as a single lease component for all of the Company’s leases.

Adoption of ASU 2016-02 resulted in recognition of a ROU asset of $2.8 million and an operating lease liability of $6.2 million, related to the lease of office and laboratory space; and the derecognition of deferred rent of $3.4 million for certain lease incentives received previously. The comparative prior period information continues to be reported under the accounting standards in effect during those periods.

ASU 2018-07

In June 2018, the FASB issued ASU 2018-07, “Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting” (“ASU 2018-07”), which expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees and applies to all share-based payment transactions in which a grantor acquires goods or services to be used or consumed in a grantor’s own operations by issuing share-based payment awards. ASU 2018-07 was adopted by the Company on January 1, 2019 using the modified retrospective transition method with no impact on the condensed consolidated financial statements. As a result of adopting ASU 2018-07, the estimated fair values of stock awards issued to non-employees are determined at issuance and are no longer subject to revaluation over their vesting terms.

Recent Accounting Pronouncements

ASU 2018-13

In August 2018, the FASB issued ASU 2018-13, “Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement,” which improves the effectiveness of the disclosures required under ASC 820, “Fair Value Measurements and Disclosures” and modifies the disclosure requirements on fair value measurements, including the consideration of costs and benefits. The new standard is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years, and early adoption is permitted. The Company is currently evaluating the impact of the pending adoption of this new standard on its consolidated financial statements.

Investment Securities

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Investment Securities

3. INVESTMENT SECURITIES

The Company reports its available-for-sale investment securities at their estimated fair values based on quoted market prices for identical or similar instruments. The following is a summary of the available-for-sale investment securities held by the Company as of June 30, 2019 and December 31, 2018 (in thousands):

	As of June 30, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Market Value
Available-for-sale investment securities:
U.S. government and agency obligations	$	41,410	$	163	$	—	$	41,573
Certificates of deposit		5,909		52		—		5,961
Commercial paper		24,603		—		—		24,603
Corporate debt securities		13,102		19		—		13,121
Total	$	85,024	$	234	$	—	$	85,258

	As of December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Market Value
Available-for-sale investment securities:
U.S. government and agency obligations	$	42,193	$	72	$	(1	)	$	42,264
Certificates of deposit		5,408		—		—			5,408
Commercial paper		47,686		—		—			47,686
Corporate debt securities		23,554		2		(12	)		23,544
Total	$	118,841	$	74	$	(13	)	$	118,902

All available-for-sale investment securities held at June 30, 2019 and December 31, 2018, had maturity dates of less than 24 months.

None of the Company’s available-for-sale investment securities were in a material unrealized loss position at June 30, 2019 or December 31, 2018. As such, the Company has not recognized any impairment in its financial statements related to its available-for-sale investment securities.

Fair Value Measurements

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

4. FAIR VALUE MEASUREMENTS

The Company holds investment securities that consist of highly liquid, investment grade debt securities. The Company determines the fair value of its investment securities based upon one or more valuations reported by its investment accounting and reporting service provider. The investment service provider values the securities using a hierarchical security pricing model that relies primarily on valuations provided by an industry-recognized valuation service. Such valuations may be based on trade prices in active markets for identical assets or liabilities (Level 1 inputs) or valuation models using inputs that are observable either directly or indirectly (Level 2 inputs), such as quoted prices for similar assets or liabilities, yield curves, volatility factors, credit spreads, default rates, loss severity, current market and contractual prices for the underlying instruments or debt, and broker and dealer quotes, as well as other relevant economic measures.

Financial assets measured at fair value on a recurring basis as of June 30, 2019 and December 31, 2018 were as follows (in thousands):

	As of June 30, 2019
	Level 1		Level 2		Level 3		Total
Investment securities:
U.S. government and agency obligations	$	23,405	$	18,168	$	—	$	41,573
Certificates of deposit		—		5,961		—		5,961
Commercial paper		—		24,603		—		24,603
Corporate debt securities		—		13,121		—		13,121
Total assets measured at fair value	$	23,405	$	61,853	$	—	$	85,258

	As of December 31, 2018
	Level 1		Level 2		Level 3		Total
Investment securities:
U.S. government and agency obligations	$	22,275	$	19,989	$	—	$	42,264
Certificates of deposit		—		5,408		—		5,408
Commercial paper		—		47,686		—		47,686
Corporate debt securities		—		23,544		—		23,544
Total assets measured at fair value	$	22,275	$	96,627	$	—	$	118,902

The Company’s policy is to recognize transfers between levels of the fair value hierarchy on the date of the event or change in circumstances that caused the transfer. There were no transfers into or out of Level 3 during the six months ended June 30, 2019.

- Definition

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

+ References + Details

Balance Sheet Details

6 Months Ended

Jun. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Details

5. BALANCE SHEET DETAILS

Prepaid expenses and other current assets consist of the following (in thousands):

	June 30, 2019		December 31, 2018
Prepaid research and development costs	$	1,656	$	8
SBIR grant receivable		—		568
Interest receivable		300		340
Australian tax incentive receivable		265		1,016
Prepaid expenses and other assets		563		876
Total	$	2,784	$	2,808

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

	June 30, 2019			December 31, 2018
Leasehold improvements	$	3,494		$	3,494
Lab equipment		1,373			915
Office equipment		523			523
Computers and software		41			41
Property and equipment at cost		5,431			4,973
Accumulated depreciation and amortization		(1,167	)		(741	)
Total	$	4,264		$	4,232

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

	June 30, 2019		December 31, 2018
Accrued research and development costs	$	1,899	$	3,634
Short-term operating lease liability		678		—
Other accrued expenses		666		556
Total	$	3,243	$	4,190

Operating Lease

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Operating Lease

6. OPERATING LEASE

2018 Operating Lease. In February 2018, as amended in March 2018, the Company entered into a non-cancelable operating lease for a new facility in San Diego, California. The lease has an initial term of seven years which expires in August 2025, and the Company has an option to extend the term of the lease for an additional five years and has a termination option subject to early termination fees. The lease is subject to base lease payments and additional charges for common area maintenance and other costs and includes certain lease incentives and tenant improvement allowances. Rent expense is being recognized on a straight-line basis over the term of the lease. The Company’s incremental borrowing rate of 8.0% was used in its present value calculation as the facility lease does not have a stated rate, and the implicit rate was not readily determinable.

Under the terms of the lease, the Company provided the lessor with an irrevocable letter of credit in the amount of $0.5 million. The lessor is entitled to draw on the letter of credit in the event of any default by the Company under the terms of the lease.

Future Minimum Payments. As of June 30, 2019, future minimum payments under non-cancellable operating leases were as follows (in thousands):

Year ending December 31,	Minimum Payments
2019 (6 months)	$	552
2020		1,123
2021		1,173
2022		1,208
2023		1,244
Thereafter		2,151
Total future minimum lease payments		7,451
Less imputed interest		1,547
Total operating lease liability		5,904
Less current operating lease liability		678
Non-current operating lease liability	$	5,226

Rent expense was $0.3 million and $0.1 million for the three months ended June 30, 2019 and 2018, respectively, and $0.5 million and $0.2 million for the six months ended June 30, 2019 and 2018, respectively. Cash paid for amounts included in the measurement of lease liabilities for operating cash flow from operating leases was $0.3 million for the six months ended June 30, 2019.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

7. COMMITMENTS AND CONTINGENCIES

Litigation

From time to time, the Company may be subject to various claims and suits arising in the ordinary course of business. The Company does not expect that the resolution of these matters will have a material adverse effect on its financial position or results of operations.

Convertible Preferred Stock

6 Months Ended

Jun. 30, 2019

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

8. CONVERTIBLE PREFERRED STOCK

As of January 1, 2018, the Company had 28,763,179 shares of Series A convertible preferred stock outstanding. In February and March 2018, the Company issued an aggregate of 19,641,200 shares of its Series B convertible preferred stock for total proceeds of $63.5 million, net of issuance costs of $0.2 million. The holders of the Company’s Series A and B convertible preferred stock were entitled to certain customary preferences, such as dividend and liquidation priority in relationship to the common shareholders, and certain anti-dilution protection. The convertible preferred stock was classified outside of stockholders’ equity (deficit) because the shares contained certain redemption features that were not solely within the control of the Company.

In connection with the Company’s initial public offering in July 2018, all of these shares of convertible preferred stock automatically converted into 14,712,571 shares of common stock.

Equity Incentive Plans

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity Incentive Plans

9. EQUITY INCENTIVE PLANS

2018 Incentive Award Plan

In July 2018, the Company adopted the 2018 Incentive Award Plan (the “2018 Plan”). Under the 2018 Plan, which expires in July 2028, the Company may grant equity-based awards to individuals who are employees, officers, directors or consultants of the Company. Options issued under the 2018 Plan, will generally expire ten years from the date of grant and vest over a four-year period. As of June 30, 2019, 2,331,772 shares were available for future issuance under the 2018 Plan.

The 2018 Plan contains a provision that allows annual increases in the number of shares available for issuance on the first day of each calendar year through January 1, 2028 in an amount equal to the lesser of: (i) 5% of the aggregate number of shares of the Company’s common stock outstanding on December 31 of the immediately preceding calendar year, or (ii) such lesser amount determined by the Company.

2015 Stock Incentive Plan

In February 2015, the Company adopted the Crinetics Pharmaceuticals, Inc. 2015 Stock Incentive Plan (the “2015 Plan”), which provided for the issuance of equity awards to the Company’s employees, members of its board of directors and consultants. In general, options issued under this plan vest over four years and expire after 10 years. Subsequent to the adoption of the 2018 Plan, no additional equity awards can be made under the 2015 Plan.

Certain awards under the 2015 Plan allowed for exercise prior to vesting. Shares issued under such early-exercise provisions are subject to repurchase by the Company until they become fully vested. As of June 30, 2019, 49,718 unvested shares issued under early-exercise provisions were subject to repurchase by the Company. The condensed consolidated balance sheet reflects an unvested stock liability of $0.1 million as of June 30, 2019.

2018 Employee Stock Purchase Plan

In July 2018, the Company adopted the 2018 Employee Stock Purchase Plan (the “ESPP”). The ESPP permits participants to purchase common stock through payroll deductions of up to 20% of their eligible compensation. As of June 30, 2019, an aggregate of 447,061 shares of common stock were available for issuance under the ESPP.

The ESPP contains a provision that allows annual increases in the number of shares available for issuance on the first day of each calendar year through January 1, 2028 in an amount equal to the lesser of: (i) 1% of the aggregate number of shares of the Company’s common stock outstanding on December 31 of the immediately preceding calendar year, or (ii) such lesser amount determined by the Company.

Stock Options

Stock option activity during the six months ended June 30, 2019 under both of the 2015 Plan and the 2018 Plan is as follows:

				Weighted-		Weighted-		Aggregate
				Average		Average		Intrinsic
	Options			Exercise		Remaining		Value
	Outstanding			Price		Term		(000’s)
Balance at December 31, 2018		2,339,157		$	6.40
Granted		773,125		$	24.84
Cancelled		(9,119	)	$	9.28
Exercised		(63,014	)	$	1.39
Balance at June 30, 2019		3,040,149		$	11.18		8.8	$	42,418
Exercisable at June 30, 2019		776,012		$	5.39		8.2	$	15,224

The aggregate intrinsic value in the above table is calculated as the difference between the closing price of our common stock at June 30, 2018 and the exercise price of stock options that had strike prices below the closing price. The total intrinsic value of options exercised during the first six months of 2019 was $1.5 million.

Fair Value of Stock Option Awards

The Company utilizes the Black-Scholes option pricing model to value awards under its equity plans. The following table summarizes the weighted average assumptions used to estimate the fair value of stock options granted to employees under the Company’s stock option plans and the shares purchasable under the ESPP during the periods presented:

Stock Option Plans	2019	2018
Expected life of option	5.9 years	6.0 years
Volatility	78%	70%
Risk free interest rate	2.4%	2.8%
Dividend yield	—%	—%

Employee Stock Purchase Plan	2019	2018
Expected life of option	1.3 years	N/A
Volatility	62%	N/A
Risk free interest rate	2.3%	N/A
Dividend yield	—%	N/A

The key assumptions used in determining the fair value of equity awards, and the Company’s rationale, were as follows: (i) Expected term - the expected term represents the period that options are expected to be outstanding and has been estimated using the simplified method, which is an average of the contractual option term and its vesting period; (ii) Expected volatility - the expected volatility assumption is based on volatilities of a peer group of similar companies in the biotechnology industry whose share prices are publicly available; (iii) Risk-free interest rate - the risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant for zero coupon U.S. Treasury notes with maturities that approximate the expected terms of awards; and (iv) Expected dividend yield - the expected dividend yield assumption is zero as the Company has never paid cash dividends and has no present intention to do so in the near future.

The weighted-average fair value of stock options granted to employees during the first half of 2019 and 2018 was $16.95 and $4.02 per share, respectively.

Stock-Based Compensation Expense

Stock-based compensation expense for the equity awards issued by the Company to employees and non-employees for the periods presented below was as follows (in thousands):

	Three months ended June 30,				Six months ended June 30,
	2019		2018		2019		2018
Included in research and development	$	839	$	130	$	1,378	$	291
Included in general and administrative		742		141		1,231		407
Total	$	1,581	$	271	$	2,609	$	698

Unrecognized stock-based compensation cost related to option awards was $20.0 million as of June 30, 2019, which is expected to be recognized over a remaining weighted-average period of approximately 2.8 years.

Unrecognized stock-based compensation cost related to the ESPP was $0.5 million as of June 30, 2019, which is expected to be recognized over a remaining weighted-average period of approximately 1.2 years.

Net Loss Per Share

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Net Loss Per Share

10. NET LOSS PER SHARE

Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows in common stock equivalent shares (in thousands):

	June 30,
	2019		2018
Convertible preferred stock outstanding		—		14,713
Common stock options		3,040		2,275
Unvested common stock subject to repurchase		50		139
		3,090		17,127

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2019
Accounting Policies [Abstract]
Description of Business	Description of Business Crinetics Pharmaceuticals, Inc. (the “Company”) is a clinical stage pharmaceutical company incorporated in Delaware on November 18, 2008 and based in San Diego, California. The Company is focused on the discovery, development and commercialization of novel therapeutics for rare endocrine diseases and endocrine-related tumors. In January 2017, the Company established a wholly owned Australian subsidiary, Crinetics Australia Pty Ltd (“CAPL”), in order to conduct various preclinical and clinical activities for its development candidates. On July 6, 2018, the Company effected a 1-for-3.29 reverse stock split of its common stock. The par value and the authorized shares of the common stock were not adjusted as a result of the reverse stock split. The reverse stock split resulted in an adjustment to the conversion prices of the Company’s Series A and B preferred stock to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying condensed consolidated financial statements and notes to the condensed consolidated financial statements give retroactive effect to the reverse stock split for all periods presented.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying interim condensed consolidated balance sheet as of June 30, 2019, the condensed consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2019 and 2018, the condensed consolidated statements of convertible preferred stock and stockholders’ equity (deficit) for the three and six months ended June 30, 2019 and 2018, and the condensed consolidated statements of cash flows for the six months ended June 30, 2019 and 2018, and the related disclosures are unaudited. In management’s opinion, the unaudited interim financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of June 30, 2019 and the results of its operations and cash flows for the six months ended June 30, 2019 and 2018 in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The results for the three and six months ended June 30, 2019 are not necessarily indicative of the results expected for the full fiscal year or any other interim period.
Principles of Consolidation and Foreign Currency Transactions	Principles of Consolidation and Foreign Currency Transactions The condensed consolidated financial statements include the accounts of the Company and CAPL. All intercompany accounts and transactions have been eliminated in consolidation. The functional currency of both the Company and CAPL is the U.S. dollar. Assets and liabilities that are not denominated in the functional currency are remeasured into U.S. dollars at foreign currency exchange rates in effect at the balance sheet date except for nonmonetary assets, which are remeasured at historical foreign currency exchange rates in effect at the date of transaction. Net realized and unrealized gains and losses from foreign currency transactions and remeasurement are reported in other income (expense), in the condensed consolidated statements of operations and were not material for all periods presented.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.
Liquidity and Going Concern	Liquidity and Going Concern From inception, the Company has devoted substantially all of its efforts to drug discovery and development and conducting preclinical studies and clinical trials. The Company has a limited operating history and the sales and income potential of the Company’s business and market are unproven. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. As of June 30, 2019, the Company had $145.0 million in unrestricted cash, cash equivalents and investment securities. The Company believes it has sufficient cash to meet its funding requirements for at least the next 12 months. However, the Company has experienced net losses and negative cash flows from operating activities since its inception and has an accumulated deficit of $64.8 million as of June 30, 2019. The Company expects to continue to incur net losses for the foreseeable future and believes it will need to raise substantial additional capital to accomplish its business plan over the next several years. The Company plans to continue to fund its losses from operations and capital funding needs through a combination of equity offerings, debt financings or other sources, including potential collaborations, licenses and other similar arrangements. If the Company is not able to secure adequate additional funding, the Company may be forced to make reductions in spending, extend payment terms with suppliers, liquidate assets where possible, or suspend or curtail planned programs. Any of these actions could materially harm the Company’s business, results of operations and future prospects. There can be no assurance as to the availability or terms upon which such financing and capital might be available in the future.
Use of Estimates	Use of Estimates The Company’s condensed consolidated financial statements are prepared in accordance with U.S. GAAP. The preparation of the Company’s condensed consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Company’s condensed consolidated financial statements and accompanying notes. The most significant estimates in the Company’s condensed consolidated financial statements relate to revenue recognition, accrued amounts receivable under the Australian research and development tax incentive program, accrued expenses and associated research and development expense, the assumptions underlying the determination of the estimated incremental borrowing rate for the determination of the operating lease right-of-use asset, and the assumptions underlying the determination of the fair value of equity awards for purposes of determining stock-based compensation. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.
Fair Value Measurements	Fair Value Measurements The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or non-recurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets. Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly. Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. The carrying amounts of the Company’s current financial assets, restricted cash and current financial liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts. Restricted cash represents cash held as collateral for the Company’s facility lease and is reported as a long-term asset in the accompanying condensed consolidated balance sheets.
Investment Securities	Investment Securities All investments have been classified as “available-for-sale” and are carried at fair value as determined based upon quoted market prices or pricing models for similar securities at period end. Investments with contractual maturities less than 12 months at the balance sheet date are considered short-term investments. Investments with contractual maturities beyond one year are also classified as short-term due to the Company’s ability to liquidate the investment for use in operations within the next 12 months. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold. The Company has not realized any significant gains or losses on sales of available-for-sale investment securities during any of the periods presented. Unrealized gains and losses that are determined to be temporary in nature are reported as a component of accumulated other comprehensive income (loss). A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the establishment of a new cost basis for the security. Interest income is recognized when earned and includes the amortization of purchase premiums and accretion of purchase discounts.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash balances due to the financial position of the depository institution in which those deposits are held. Additionally, the Company has established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity.
Leases	Leases The Company determines if an arrangement is a lease at the inception of the arrangement. Leases with a term longer than 12 months that are determined to be operating leases are included in operating lease assets, accrued expenses and other current liabilities and noncurrent operating lease liabilities in the condensed consolidated balance sheets based on the present value of the minimum lease payments called for under the arrangement. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.
Grant Revenue Recognition	Grant Revenue Recognition The Company’s grant revenues are derived from Small Business Innovation Research (“SBIR”) grants from the National Institutes of Health. The Company recognizes SBIR grant revenue as reimbursable grant costs are incurred. The costs associated with these reimbursements are reflected as a component of research and development expense in the accompanying condensed consolidated statements of operations. Earnings in excess of billings are included as a component of prepaid expenses and other current assets.
Research and Development Expenses	Research and Development Expenses Research and development (“R&D”) expenses consist primarily of salaries, payroll taxes, employee benefits and stock-based compensation charges for those individuals involved in R&D efforts, as well as consulting expenses, third-party R&D expenses, laboratory supplies, clinical materials and overhead, including facilities and depreciation costs, offset by the Australian Tax Incentive discussed below. R&D expenses are charged to expense as incurred. Payments made prior to the receipt of goods or services to be used in R&D are capitalized until the goods or services are received. Costs incurred under contracts with contract research organizations (“CROs”) that conduct and manage the Company’s clinical trials are also included in research and development expenses. The financial terms and activities of these agreements vary from contract to contract and may result in uneven expense levels. Generally, these agreements set forth activities that drive the recording of expenses such as start-up and initiation activities, enrollment and treatment of patients, or the completion of other clinical trial activities. Expenses related to clinical trials are accrued based on estimates and/or representations from service providers regarding work performed, including actual level of patient enrollment, completion of patient studies and progress of the clinical trials. Other incidental costs related to patient enrollment or treatment are accrued when reasonably certain. If the amounts that the Company is obligated to pay under its clinical trial agreements are modified (for instance, as a result of changes in the clinical trial protocol or scope of work to be performed), the Company adjusts its accruals accordingly on a prospective basis. Revisions to contractual payment obligations are charged to expense in the period in which the facts that give rise to the revision become reasonably certain.
Australian Research and Development Tax Incentive	Australian Research and Development Tax Incentive CAPL is eligible to obtain a cash refund from the Australian Taxation Office for eligible R&D expenditures under the Australian Research and Development Tax Incentive Program (the “Australian Tax Incentive”). The Australian Tax Incentive is recognized as a reduction to R&D expense when there is reasonable assurance that the Australian Tax Incentive will be received, the relevant expenditure has been incurred, and the amount can be reliably measured. The Company recognized a reduction to R&D expense of $0.2 million and $0.6 million for the three months ended June 30, 2019 and 2018, respectively, and a reduction to R&D expense of $0.3 million and $0.9 million for the six months ended June 30, 2019 and 2018, respectively.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense represents the cost of the grant date fair value of awards over the requisite service period of the awards (usually the vesting period) on a straight-line basis. For stock awards for which vesting is subject to performance-based milestones, the expense is recorded over the remaining service period after the point when the achievement of the milestone is probable, or the performance condition has been achieved. The Company estimates the fair value of all stock option grants using the Black-Scholes option pricing model and recognizes forfeitures as they occur.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is comprised of the Company’s net loss for all periods presented and the unrealized gain on investment securities held as of June 30, 2019.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of convertible preferred stock, common stock subject to repurchase, and options outstanding under the Company’s stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as inclusion of the potentially dilutive securities would be antidilutive.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements ASU 2016-02 In February 2016, the Financial Accounting Standards Board issued Accounting Standards Update (“ASU”) 2016-02, “Leases (Topic 842)” (“ASU 2016-02”) which requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. ASU 2016-02 establishes a right-of-use (ROU) model that requires a lessee to recognize a ROU asset and lease liability on the balance sheet for all leases with a term longer than 12 months. ASU 2016-02 also requires disclosures to meet the objective of enabling users of financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. On January 1, 2019, the Company adopted ASU 2016-02 using the modified retrospective transition method. Under this transition method, the Company recognized and measured leases that existed at the adoption date in the condensed consolidated balance sheet as of January 1, 2019. ROU assets represent the right to use an underlying asset for the lease term and lease liabilities represent the obligation to make lease payments arising from the lease. Operating lease ROU assets and operating lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term, discounted at the rate implicit in the lease. If the rate implicit in the lease cannot be determined, Topic 842 requires the use of the rate of interest that a lessee would have to pay to borrow on a collateralized basis over a similar term for a similar amount to the lease payments in a similar economic environment. The operating lease ROU asset is also adjusted for any prepaid or accrued lease payments and any lease incentives received. Operating lease terms may include options to extend or terminate the lease when it is reasonably certain that these options will be exercised. Further, the Company has elected to recognize short-term lease payments on a straight-line basis over the associated lease term and variable lease payments in the period in which the obligation for those payments is incurred. Short-term and variable lease payments were not material in the first half of 2019. In connection with the adoption of ASU 2016-02, the Company elected the package of practical expedients requiring no reassessment of whether any expired or existing contracts contain leases, the lease classification of any expired or existing leases, or initial direct costs for any existing leases. The Company also made accounting policy elections not to apply the recognition requirements under ASU 2016-02 to any short-term leases and to account for each separate lease and associated non-lease components as a single lease component for all of the Company’s leases. Adoption of ASU 2016-02 resulted in recognition of a ROU asset of $2.8 million and an operating lease liability of $6.2 million, related to the lease of office and laboratory space; and the derecognition of deferred rent of $3.4 million for certain lease incentives received previously. The comparative prior period information continues to be reported under the accounting standards in effect during those periods. ASU 2018-07 In June 2018, the FASB issued ASU 2018-07, “Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting” (“ASU 2018-07”), which expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees and applies to all share-based payment transactions in which a grantor acquires goods or services to be used or consumed in a grantor’s own operations by issuing share-based payment awards. ASU 2018-07 was adopted by the Company on January 1, 2019 using the modified retrospective transition method with no impact on the condensed consolidated financial statements. As a result of adopting ASU 2018-07, the estimated fair values of stock awards issued to non-employees are determined at issuance and are no longer subject to revaluation over their vesting terms. Recent Accounting Pronouncements ASU 2018-13 In August 2018, the FASB issued ASU 2018-13, “Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement,” which improves the effectiveness of the disclosures required under ASC 820, “Fair Value Measurements and Disclosures” and modifies the disclosure requirements on fair value measurements, including the consideration of costs and benefits. The new standard is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years, and early adoption is permitted. The Company is currently evaluating the impact of the pending adoption of this new standard on its consolidated financial statements

Investment Securities (Tables)

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Summary of Available-For-Sale Investment Securities Held by the Company

The following is a summary of the available-for-sale investment securities held by the Company as of June 30, 2019 and December 31, 2018 (in thousands):

	As of June 30, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Market Value
Available-for-sale investment securities:
U.S. government and agency obligations	$	41,410	$	163	$	—	$	41,573
Certificates of deposit		5,909		52		—		5,961
Commercial paper		24,603		—		—		24,603
Corporate debt securities		13,102		19		—		13,121
Total	$	85,024	$	234	$	—	$	85,258

	As of December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Market Value
Available-for-sale investment securities:
U.S. government and agency obligations	$	42,193	$	72	$	(1	)	$	42,264
Certificates of deposit		5,408		—		—			5,408
Commercial paper		47,686		—		—			47,686
Corporate debt securities		23,554		2		(12	)		23,544
Total	$	118,841	$	74	$	(13	)	$	118,902

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Schedule of Financial Assets Measured at Fair Value on Recurring Basis

Financial assets measured at fair value on a recurring basis as of June 30, 2019 and December 31, 2018 were as follows (in thousands):

	As of June 30, 2019
	Level 1		Level 2		Level 3		Total
Investment securities:
U.S. government and agency obligations	$	23,405	$	18,168	$	—	$	41,573
Certificates of deposit		—		5,961		—		5,961
Commercial paper		—		24,603		—		24,603
Corporate debt securities		—		13,121		—		13,121
Total assets measured at fair value	$	23,405	$	61,853	$	—	$	85,258

	As of December 31, 2018
	Level 1		Level 2		Level 3		Total
Investment securities:
U.S. government and agency obligations	$	22,275	$	19,989	$	—	$	42,264
Certificates of deposit		—		5,408		—		5,408
Commercial paper		—		47,686		—		47,686
Corporate debt securities		—		23,544		—		23,544
Total assets measured at fair value	$	22,275	$	96,627	$	—	$	118,902

Balance Sheet Details (Tables)

6 Months Ended

Jun. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Components of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consist of the following (in thousands):

	June 30, 2019		December 31, 2018
Prepaid research and development costs	$	1,656	$	8
SBIR grant receivable		—		568
Interest receivable		300		340
Australian tax incentive receivable		265		1,016
Prepaid expenses and other assets		563		876
Total	$	2,784	$	2,808

Components of Property and Equipment

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

	June 30, 2019			December 31, 2018
Leasehold improvements	$	3,494		$	3,494
Lab equipment		1,373			915
Office equipment		523			523
Computers and software		41			41
Property and equipment at cost		5,431			4,973
Accumulated depreciation and amortization		(1,167	)		(741	)
Total	$	4,264		$	4,232

Components of Accrued Expenses

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

	June 30, 2019		December 31, 2018
Accrued research and development costs	$	1,899	$	3,634
Short-term operating lease liability		678		—
Other accrued expenses		666		556
Total	$	3,243	$	4,190

Operating Lease (Tables)

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Schedule of Future Minimum Payments Under Non-cancellable Operating Leases

As of June 30, 2019, future minimum payments under non-cancellable operating leases were as follows (in thousands):

Year ending December 31,	Minimum Payments
2019 (6 months)	$	552
2020		1,123
2021		1,173
2022		1,208
2023		1,244
Thereafter		2,151
Total future minimum lease payments		7,451
Less imputed interest		1,547
Total operating lease liability		5,904
Less current operating lease liability		678
Non-current operating lease liability	$	5,226

Equity Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity under 2015 Plan and 2018 Plan

Stock option activity during the six months ended June 30, 2019 under both of the 2015 Plan and the 2018 Plan is as follows:

				Weighted-		Weighted-		Aggregate
				Average		Average		Intrinsic
	Options			Exercise		Remaining		Value
	Outstanding			Price		Term		(000’s)
Balance at December 31, 2018		2,339,157		$	6.40
Granted		773,125		$	24.84
Cancelled		(9,119	)	$	9.28
Exercised		(63,014	)	$	1.39
Balance at June 30, 2019		3,040,149		$	11.18		8.8	$	42,418
Exercisable at June 30, 2019		776,012		$	5.39		8.2	$	15,224

Weighted Average Assumptions Used to Estimate Fair Value of Stock Options Granted to Employees

Stock Option Plans	2019	2018
Expected life of option	5.9 years	6.0 years
Volatility	78%	70%
Risk free interest rate	2.4%	2.8%
Dividend yield	—%	—%

Employee Stock Purchase Plan	2019	2018
Expected life of option	1.3 years	N/A
Volatility	62%	N/A
Risk free interest rate	2.3%	N/A
Dividend yield	—%	N/A

Summary of Stock-based Compensation Expense for the Equity Awards Issued to Employees and Non-Employees

Stock-based compensation expense for the equity awards issued by the Company to employees and non-employees for the periods presented below was as follows (in thousands):

	Three months ended June 30,				Six months ended June 30,
	2019		2018		2019		2018
Included in research and development	$	839	$	130	$	1,378	$	291
Included in general and administrative		742		141		1,231		407
Total	$	1,581	$	271	$	2,609	$	698

Net Loss Per Share (Tables)

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share

Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows in common stock equivalent shares (in thousands):

	June 30,
	2019		2018
Convertible preferred stock outstanding		—		14,713
Common stock options		3,040		2,275
Unvested common stock subject to repurchase		50		139
		3,090		17,127

Organization and Basis of Presentation - Additional Information (Details) $ in Thousands		6 Months Ended
	Jul. 06, 2018	Jun. 30, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)
Organization And Basis Of Presentation [Line Items]
Number of operating segments \| Segment		1
Unrestricted cash, cash equivalents and investments securities		$ 145,000
Accumulated deficit		$ 64,823	$ 43,380
Minimum
Organization And Basis Of Presentation [Line Items]
Period of sufficient cash to meet its funding requirements		12 months
Common Stock
Organization And Basis Of Presentation [Line Items]
Stock reverse stock split	1-for-3.29
Stock split conversion ratio	0.3040

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Summary Of Significant Accounting Policies [Line Items]
Operating lease right-of-use asset	$ 2,627		$ 2,627
Operating Lease, Liability	5,904		5,904
ASU 2016-02
Summary Of Significant Accounting Policies [Line Items]
Operating lease right-of-use asset	2,800		2,800
Operating Lease, Liability	6,200		6,200
Deferred rent	3,400		3,400
Australian Research and Development Tax Incentive \| Australian Taxation Office
Summary Of Significant Accounting Policies [Line Items]
Tax incentive receivable, reductions to research and development expense	$ 200	$ 600	$ 300	$ 900

Investment Securities - Summary of Available-For-Sale Investment Securities Held by the Company (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Amortized Cost	$ 85,024	$ 118,841
Available-for-sale investment securities, Gross Unrealized Gains	234	74
Available-for-sale investment securities, Gross Unrealized Losses		(13)
Available-for-sale investment securities, Fair Market Value	85,258	118,902
U.S. Government and Agency Obligations
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Amortized Cost	41,410	42,193
Available-for-sale investment securities, Gross Unrealized Gains	163	72
Available-for-sale investment securities, Gross Unrealized Losses		(1)
Available-for-sale investment securities, Fair Market Value	41,573	42,264
Certificates of Deposit
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Amortized Cost	5,909	5,408
Available-for-sale investment securities, Gross Unrealized Gains	52
Available-for-sale investment securities, Fair Market Value	5,961	5,408
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Amortized Cost	24,603	47,686
Available-for-sale investment securities, Fair Market Value	24,603	47,686
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale investment securities, Amortized Cost	13,102	23,554
Available-for-sale investment securities, Gross Unrealized Gains	19	2
Available-for-sale investment securities, Gross Unrealized Losses		(12)
Available-for-sale investment securities, Fair Market Value	$ 13,121	$ 23,544

Investment Securities - Additional Information (Details)	Jun. 30, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Available-for-sale investment securities maturity period, maximum	24 months	24 months

Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	$ 85,258	$ 118,902
Level 1
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	23,405	22,275
Level 2
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	61,853	96,627
U.S. Government and Agency Obligations
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	41,573	42,264
U.S. Government and Agency Obligations \| Level 1
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	23,405	22,275
U.S. Government and Agency Obligations \| Level 2
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	18,168	19,989
Certificates of Deposit
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	5,961	5,408
Certificates of Deposit \| Level 2
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	5,961	5,408
Commercial Paper
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	24,603	47,686
Commercial Paper \| Level 2
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	24,603	47,686
Corporate Debt Securities
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	13,121	23,544
Corporate Debt Securities \| Level 2
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Total assets measured at fair value	$ 13,121	$ 23,544

Fair Value Measurements - Additional Information (Details)	6 Months Ended
	Jun. 30, 2019 USD ($)
Fair Value Disclosures [Abstract]
Fair value assets transferred into level 3	$ 0
Fair value assets transferred into level 3	0
Fair value assets transferred into level 3	0
Fair value assets transferred into level 3	$ 0

Balance Sheet Details - Components of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid research and development costs	$ 1,656	$ 8
SBIR grant receivable		568
Interest receivable	300	340
Australian tax incentive receivable	265	1,016
Prepaid expenses and other assets	563	876
Total	$ 2,784	$ 2,808

Balance Sheet Details - Components of Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment at cost	$ 5,431	$ 4,973
Accumulated depreciation and amortization	(1,167)	(741)
Total	4,264	4,232
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment at cost	3,494	3,494
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment at cost	1,373	915
Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment at cost	523	523
Computers and Software
Property Plant And Equipment [Line Items]
Property and equipment at cost	$ 41	$ 41

Balance Sheet Details - Components of Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued research and development costs	$ 1,899	$ 3,634
Short-term operating lease liability	678
Other accrued expenses	666	556
Total	$ 3,243	$ 4,190

Operating Lease - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating Leased Assets [Line Items]
Operating lease liability			$ (277)
2018 Operating Lease
Operating Leased Assets [Line Items]
Operating lease, initial term	7 years		7 years
Operating lease expiration period			2025-08
Operating lease, option to extend term			five years
Lessee,operating lease, discount rate	8.00%		8.00%
Irrevocable letter of credit	$ 500		$ 500
Rent expense	$ 300	$ 100	500	$ 200
Operating lease liability			$ 300

Operating Lease - Schedule of Future Minimum Payments Under Non-cancellable Operating Leases (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Leases [Abstract]
2019 (6 months)	$ 552
2020	1,123
2021	1,173
2022	1,208
2023	1,244
Thereafter	2,151
Total future minimum lease payments	7,451
Less imputed interest	1,547
Total operating lease liability	5,904
Less current operating lease liability	678
Non-current operating lease liability	$ 5,226

Convertible Preferred Stock - Additional Information (Details) - USD ($) $ in Thousands		2 Months Ended	6 Months Ended
	Jul. 20, 2018	Mar. 31, 2018	Jun. 30, 2018	Jan. 01, 2018
Temporary Equity [Line Items]
Net proceeds from issuance of convertible preferred stock			$ 63,266
Convertible preferred stock, issuance costs			$ 660
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred,Shares Outstanding				28,763,179
Series A and B Convertible Preferred Stock \| Initial Public Offering
Temporary Equity [Line Items]
Stock issued upon conversion of convertible securities	14,712,571
Series B Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued		19,641,200
Net proceeds from issuance of convertible preferred stock		$ 63,500
Convertible preferred stock, issuance costs		$ 200

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		6 Months Ended
	Jul. 31, 2018	Feb. 28, 2015	Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total intrinsic value of options exercised			$ 1.5
Dividend yield			0.00%
Weighted-average fair value of stock options granted to employees per share			$ 16.95	$ 4.02
Unrecognized stock-based compensation cost			$ 20.0
Weighted-average period of unrecognized stock-based compensation cost expected to be recognized over remaining period			2 years 9 months 18 days
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum percentage of eligible compensation to purchase common stock through payroll deductions	20.00%
Weighted-average period of unrecognized stock-based compensation cost expected to be recognized over remaining period			1 year 2 months 12 days
Unrecognized stock-based compensation cost			$ 0.5
2018 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan expiration period	2028-07
Plan expiration term	10 years
Vesting period	4 years
Plan expiration date			Jan. 01, 2028
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan expiration term		10 years
Vesting period		4 years
Shares issued under early-exercise provisions subject to repurchase			49,718
Unvested stock liability			$ 0.1
Common Stock \| ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan expiration date			Jan. 01, 2028
Shares of common stock available for issuance			447,061
Common Stock \| 2018 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining shares available for future issuance			2,331,772

Equity Incentive Plans - Summary of Stock Option Activity under 2015 Plan and 2018 Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Beginning balance	2,339,157
Options Outstanding, Granted	773,125
Options Outstanding, Cancelled	(9,119)
Options Outstanding, Exercised	(63,014)
Options Outstanding, Ending balance	3,040,149
Options Outstanding, Exercisable	776,012
Weighted-Average Exercise Price, Beginning balance	$ 6.40
Weighted-Average Exercise Price, Granted	24.84
Weighted-Average Exercise Price, Cancelled	9.28
Weighted Average Exercise Price, Exercised	1.39
Weighted-Average Exercise Price, Ending balance	11.18
Weighted-Average Exercise Price, Exercisable	$ 5.39
Weighted-Average Remaining Term, Ending balance	8 years 9 months 18 days
Weighted-Average Remaining Term, Exercisable	8 years 2 months 12 days
Aggregate Intrinsic Value, Ending balance	$ 42,418
Aggregate Intrinsic Value, Exercisable	$ 15,224

Equity Incentive Plans - Weighted Average Assumptions Underlying Fair Value Calculations for Stock Option Awards (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life of option	1 year 3 months 18 days
Volatility	62.00%
Risk free interest rate	2.30%
Stock Options Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life of option	5 years 10 months 24 days	6 years
Volatility	78.00%	70.00%
Risk free interest rate	2.40%	2.80%

Equity Incentive Plans - Stock-based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,581	$ 271	$ 2,609	$ 698
Included in Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	839	130	1,378	291
Included in General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 742	$ 141	$ 1,231	$ 407

Net Loss Per Share - Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities (in common stock equivalent shares) excluded from calculation of diluted net loss per share	3,090	17,127
Convertible Preferred Stock Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities (in common stock equivalent shares) excluded from calculation of diluted net loss per share		14,713
Common Stock Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities (in common stock equivalent shares) excluded from calculation of diluted net loss per share	3,040	2,275
Unvested Common Stock Subject to Repurchase
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities (in common stock equivalent shares) excluded from calculation of diluted net loss per share	50	139