Kodiak Sciences (KOD) 10-Q 14 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	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	KOD
Entity Registrant Name	Kodiak Sciences Inc.
Entity Central Index Key	0001468748
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		36,931,141
Entity File Number	001-38682
Entity Tax Identification Number	270476525
Entity Address, Address Line One	2631 Hanover Street
Entity Address, City or Town	Palo Alto
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94304
City Area Code	650
Local Phone Number	281-0850

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 44,967	$ 88,254
Marketable securities	23,134
Prepaid expenses and other current assets	2,391	2,195
Total current assets	70,492	90,449
Restricted cash	140	140
Property and equipment, net	1,238	1,097
Operating lease right-of-use asset	1,981
Other assets	4,424	503
Total assets	78,275	92,189
Current liabilities:
Accounts payable	2,529	1,050
Accrued and other current liabilities	3,277	3,776
Operating lease liability	408
Total current liabilities	6,214	4,826
Operating lease liability, net of current portion	1,725
Other liabilities	317	530
Total liabilities	8,256	5,356
Commitments and contingencies (Note 6)
Stockholders’ equity:
Common stock, $0.0001 par value, 490,000,000 shares authorized at June 30, 2019 and December 31, 2018; 36,931,141 and 36,829,857 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	4	4
Additional paid-in capital	200,138	197,595
Accumulated other comprehensive loss	12
Accumulated deficit	(130,135)	(110,766)
Total stockholders’ equity	70,019	86,833
Total liabilities and stockholders’ equity	$ 78,275	$ 92,189

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) (unaudited) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	490,000,000	490,000,000
Common stock, shares issued	36,931,141	36,829,857
Common stock, shares outstanding	36,931,141	36,829,857

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses
Research and development	$ 8,838	$ 3,591	$ 14,561	$ 7,233
General and administrative	2,976	1,499	5,713	3,404
Total operating expenses	11,814	5,090	20,274	10,637
Loss from operations	(11,814)	(5,090)	(20,274)	(10,637)
Interest income	431	76	911	124
Interest expense (includes $1,005 and $1,867 attributable to related parties for the three and six months ended June 30, 2018, respectively)	(2)	(1,877)	(6)	(3,347)
Other income (expense), net (includes $191 and $1,585 other expense attributable to related parties for the three and six months ended June 30, 2018, respectively)	0	(518)	0	(2,469)
Net loss	$ (11,385)	$ (7,409)	$ (19,369)	$ (16,329)
Net loss per common share, basic and diluted	$ (0.31)	$ (0.96)	$ (0.52)	$ (2.11)
Weighted-average common shares outstanding used in computing net loss per common share, basic and diluted	37,294,853	7,757,081	37,271,638	7,720,967
Other comprehensive income
Change in unrealized gains related to available-for-sale debt securities, net of tax	$ 6	$ 0	$ 12	$ 0
Total other comprehensive income	6	0	12	0
Comprehensive loss	$ (11,379)	$ (7,409)	$ (19,357)	$ (16,329)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) (unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Income Statement [Abstract]
Interest expense attributable to related parties	$ 1,005	$ 1,867
Other expense attributable to related parties	$ 191	$ 1,585

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2017	$ (68,738)		$ 1	$ 584		$ (69,323)
Redeemable convertible preferred stock, shares outstanding, beginning balance at Dec. 31, 2017		12,385,154
Redeemable convertible preferred stock, beginning balance at Dec. 31, 2017		$ 50,017
Beginning balance, shares at Dec. 31, 2017			7,936,434
Issuance of common stock upon exercise of stock options, shares			300
Stock-based compensation expense	92			92
Net loss	(8,920)					(8,920)
Ending Balance at Mar. 31, 2018	(77,566)		$ 1	676		(78,243)
Redeemable convertible preferred stock, shares outstanding, ending balance at Mar. 31, 2018		12,385,154
Redeemable convertible preferred stock, ending balance at Mar. 31, 2018		$ 50,017
Ending balance, shares at Mar. 31, 2018			7,936,734
Beginning Balance at Dec. 31, 2017	(68,738)		$ 1	584		(69,323)
Redeemable convertible preferred stock, shares outstanding, beginning balance at Dec. 31, 2017		12,385,154
Redeemable convertible preferred stock, beginning balance at Dec. 31, 2017		$ 50,017
Beginning balance, shares at Dec. 31, 2017			7,936,434
Total other comprehensive income	0
Net loss	(16,329)
Ending Balance at Jun. 30, 2018	(84,227)		$ 1	1,424		(85,652)
Redeemable convertible preferred stock, shares outstanding, ending balance at Jun. 30, 2018		12,385,154
Redeemable convertible preferred stock, ending balance at Jun. 30, 2018		$ 50,017
Ending balance, shares at Jun. 30, 2018			7,964,234
Beginning Balance at Mar. 31, 2018	(77,566)		$ 1	676		(78,243)
Redeemable convertible preferred stock, shares outstanding, beginning balance at Mar. 31, 2018		12,385,154
Redeemable convertible preferred stock, beginning balance at Mar. 31, 2018		$ 50,017
Beginning balance, shares at Mar. 31, 2018			7,936,734
Issuance of restricted stock awards, shares			27,500
Stock-based compensation expense	748			748
Total other comprehensive income	0
Net loss	(7,409)					(7,409)
Ending Balance at Jun. 30, 2018	(84,227)		$ 1	1,424		(85,652)
Redeemable convertible preferred stock, shares outstanding, ending balance at Jun. 30, 2018		12,385,154
Redeemable convertible preferred stock, ending balance at Jun. 30, 2018		$ 50,017
Ending balance, shares at Jun. 30, 2018			7,964,234
Beginning Balance at Dec. 31, 2018	86,833		$ 4	197,595		(110,766)
Beginning balance, shares at Dec. 31, 2018			36,829,857
Issuance of common stock upon exercise of stock options	83			83
Issuance of common stock upon exercise of stock options, shares			80,000
Stock-based compensation expense	1,157			1,157
Total other comprehensive income	6				$ 6
Net loss	(7,984)					(7,984)
Ending Balance at Mar. 31, 2019	80,095		$ 4	198,835	6	(118,750)
Ending balance, shares at Mar. 31, 2019			36,909,857
Beginning Balance at Dec. 31, 2018	86,833		$ 4	197,595		(110,766)
Beginning balance, shares at Dec. 31, 2018			36,829,857
Total other comprehensive income	12
Net loss	(19,369)
Ending Balance at Jun. 30, 2019	70,019		$ 4	200,138	12	(130,135)
Ending balance, shares at Jun. 30, 2019			36,931,141
Beginning Balance at Mar. 31, 2019	80,095		$ 4	198,835	6	(118,750)
Beginning balance, shares at Mar. 31, 2019			36,909,857
Issuance of common stock upon exercise of stock options	59			59
Issuance of common stock upon exercise of stock options, shares			21,284
Stock-based compensation expense	1,244			1,244
Total other comprehensive income	6				6
Net loss	(11,385)					(11,385)
Ending Balance at Jun. 30, 2019	$ 70,019		$ 4	$ 200,138	$ 12	$ (130,135)
Ending balance, shares at Jun. 30, 2019			36,931,141

Condensed Consolidated Statem_4

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	$ (19,369)	$ (16,329)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	260	244
Non-cash interest expense and amortization of debt discount and issuance cost	0	3,333
Change in fair value of redeemable convertible preferred stock warrant liability	0	1,705
Change in fair value of derivative instrument	0	764
Stock-based compensation	2,401	749
Accretion of discount on available-for-sale securities	(118)	0
Changes in assets and liabilities:
Prepaid expenses and other current assets	(152)	(265)
Operating lease right-of-use asset	182	0
Other assets	(4,059)	0
Accounts payable	1,342	(1,845)
Accrued and other current liabilities	(459)	(4,085)
Operating lease liability	(185)
Other liabilities		22
Net cash used in operating activities	(20,157)	(15,707)
Cash flows from investing activities
Purchase of property and equipment	(126)	(38)
Purchase of available-for-sale securities	(35,066)	0
Proceeds from maturities of available-for-sale securities	12,000	0
Net cash used in investing activities	(23,192)	(38)
Cash flows from financing activities
Proceeds from issuance of convertible notes (includes $9,560 from related parties for the six months ended June 30, 2018)		33,000
Deferred offering costs	0	(768)
Debt issuance cost	0	(140)
Proceeds from issuance of common stock	114	0
Principal payments of capital lease	(34)	(54)
Principal payments of tenant improvement allowance payable	(18)	(47)
Net cash provided by financing activities	62	31,991
Net increase (decrease) in cash, cash equivalents and restricted cash	(43,287)	16,246
Cash, cash equivalents and restricted cash, at beginning of period	88,394	1,535
Cash, cash equivalents and restricted cash, at end of period	45,107	17,781
Reconciliation of cash, cash equivalents and restricted cash to statement of financial position
Cash and cash equivalents	44,967	17,641
Restricted cash	140	140
Cash, cash equivalents and restricted cash, at end of period	45,107	17,781
Supplemental disclosures of non-cash investing and financing information:
Purchase of property and equipment under accounts payable	$ 137
Issuance of derivative instrument related to convertible notes payable		6,603
Unpaid offering costs		1,295
Deferred offering costs paid in restricted stock awards		$ 91

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Statement Of Cash Flows [Abstract]
Proceeds from issuance of convertible notes	$ 9,560

The Company

The Company	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company	1. The Company Kodiak Sciences Inc. (the “Company”) is a clinical-stage biopharmaceutical company specializing in novel therapeutics to treat high-prevalence ophthalmic diseases. The Company devotes substantially all of its time and efforts to performing research and development, raising capital and recruiting personnel. Liquidity In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern The Company has historically financed its operations primarily through the sale of redeemable convertible preferred stock, convertible notes, warrants and the sale of common stock in its initial public offering (“IPO”). To date, none of the Company’s product candidates have been approved for sale and therefore, the Company has not generated any revenue from product sales. Management expects operating losses to continue for the foreseeable future. The Company currently plans to raise additional funding as required based on the status of its development programs and projected cash flows, and The uncertainties inherent in the Company’s future operations and in its ability to obtain additional funding raise substantial doubt about its ability to continue as a going concern beyond one year from the date these financial statements are issued. The financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Summary of Significant Accounti

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 Basis of Presentation and Principles of Consolidation The accompanying condensed consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) applicable to interim periods and, in the opinion of management, include all normal and recurring adjustments which are necessary to present fairly the Company's financial position and results of operations for the reported periods. The accompanying condensed consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities as of the date of the condensed consolidated financial statements and expenses during the reporting period. Actual results could differ from those estimates. Summary of Significant Accounting Policies The significant accounting policies used in preparation of these condensed consolidated financial statements for the three and six months ended June 30, 2019 are consistent with those discussed in Note 2 to the consolidated financial statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018, except as noted below with respect to the Company’s lease and marketable securities accounting policies and as noted within the “Recent Accounting Pronouncements – Recently Adopted Accounting Pronouncements” section. Leases The Company determines if an arrangement is, or contains, a lease at inception and then classifies the lease as operating or financing based on the underlying terms and conditions of the contract. Leases with terms greater than one year are initially recognized on the balance sheet as right-of-use assets and lease liabilities based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the incremental borrowing rate, which is the rate incurred to borrow, on a collateralized basis, an amount equal to the lease payments over a similar term and in a similar economic environment. The Company has elected not to recognize leases with terms of one year or less on the balance sheet. Marketable Securities The Company invests excess cash balances in short-term marketable securities. The investments in marketable securities are classified as either held-to-maturity or available-for-sale based on facts and circumstances present at the time of purchase. Debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expensed over the life of the instrument. Equity securities with readily determinable fair values are also carried at fair value with unrealized gains and losses included in other income (expense), net. Realized gains and losses on both debt and equity securities are determined using the specific identification method and are included in other income (expense), net. If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary” and, if so, marks the investment to market through a charge to the Company’s statement of operations and comprehensive loss. Recent a p From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) ASC Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Leases (Topic 842), Codification Improvements Leases (Topic 842), Targeted Improvements Leases The Company adopted the new lease standards as of January 1, 2019 using the modified retrospective approach to recognize a cumulative-effect adjustment on the effective date and to not adjust financial information and disclosures required under the new lease standards for comparative prior periods. The Company did not elect for the package of practical expedients and assessed all contracts at the transition date. The Company did not utilize the practical expedient which allows the use of hindsight in determining lease term and assessing impairment in right-of-use assets. The Company elected to apply the practical expedient and accounted for each lease component and related non-lease component as one single component. The Company elected not to recognize leases with terms of one year or less on the balance sheet. The adoption of the new lease standards on January 1, 2019 resulted in the initial recognition of right-of-use asset of $2.2 million and operating lease liability of $2.3 million related to the operating lease for the Company’s office and laboratory space in Palo Alto, California on the consolidated balance sheets with no material impact to the consolidated statements of operations, stockholders’ equity or cash flows. Refer to Note 6. In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260) Distinguishing Liabilities from Equity (Topic 480) Derivatives and Hedging (Topic 815) (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception The Company adopted this new guidance as of January 1, 2019, which did not result in a material impact on its 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 The Company adopted this new guidance as of January 1, 2019, which did not result in a material impact on its consolidated financial statements and related disclosures. New Accounting Pronouncements Not Yet Adopted Financial Instruments - Credit Losses (Topic 362): Measurement of Credit Losses on Financial Statements which intends to improve financial reporting by requiring earlier recognition of credit losses on certain financial assets, such as available-for-sale debt securities. The standard is effective for interim and annual periods after December 15, 2019. In August 2018, the FASB issued ASU 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurements In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract,

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	6 Months Ended
	Jun. 30, 2019
Accounts Payable And Accrued Liabilities Current [Abstract]
Accrued and Other Current Liabilities	3. Accrued and Other Current Liabilities Accrued and other current liabilities consist of the following (in thousands): June 30, 2019 December 31, 2018 Accrued research and development $ 1,524 $ 1,387 Accrued salaries and benefits 1,425 2,061 Accrued legal fees 146 82 Accrued professional fees 46 117 Accrued other liabilities 136 129 Total accrued and other current liabilities $ 3,277 $ 3,776

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The following tables present the Company’s fair value hierarchy for assets measured at fair value on a recurring basis (in thousands): Fair Value Measurements at June 30, 2019 Quoted Price in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Cash equivalents: Money market funds $ 44,785 $ — $ — $ 44,785 Marketable securities: Commercial paper — 13,082 — 13,082 Corporate notes — 10,052 — 10,052 Total $ 44,785 $ 23,134 $ — $ 67,919 Fair Value Measurements at December 31, 2018 Quoted Price in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Cash equivalents: Money market funds $ 87,957 $ — $ — $ 87,957 Total $ 87,957 $ — $ — $ 87,957

Marketable Securities

Marketable Securities	6 Months Ended
	Jun. 30, 2019
Investments Debt And Equity Securities [Abstract]
Marketable Securities	5. Marketable Securities The marketable securities are classified as available-for-sale and consist of corporate notes and commercial paper. The fair value measurement data for marketable securities is obtained from independent pricing services. The Company validates the prices provided by the third-party pricing services by understanding the valuation methods and data sources used and analyzing the pricing data in certain instances. The following table summarizes the marketable securities held at June 30, 2019 (in thousands): Amortized Cost Unrealized Gains Unrealized Losses Fair Value Commercial paper $ 13,082 $ — $ — $ 13,082 Corporate notes 10,040 12 — 10,052 Total $ 23,122 $ 12 $ — $ 23,134 All marketable securities held at June 30, 2019 had contractual maturities of less than one year. There were no realized gains or losses recognized on the sale or maturity of available-for-sale debt securities during the six months ended June 30, 2019 and as a result, the Company did not reclassify any amounts out of accumulated comprehensive loss. There were no impairment charges related to marketable securities for the six months ended June 30, 2019.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Leases In January 2013, the Company executed a non-cancellable lease agreement for office and laboratory space in Palo Alto, California. The lease began in October 2013 and would expire in October 2018. In March 2016, the Company executed a lease amendment which was effective March 2016 and extended the lease term until October 2023. The Company recognized an operating lease right-of-use asset and corresponding liability on January 1, 2019 based on the present value of remaining lease payments discounted at the Company’s estimated incremental borrowing rate of 8.5% over the remaining lease term of 4.83 years. For the three and six months ended June 30, 2019, the operating lease cost was $0.1 million and $0.3 million, respectively. The operating cash flows used for operating leases was $0.3 million for the six months ended June 30, 2019. The short-term lease costs were immaterial for the three and six months ended June 30, 2019. The following tables summarize the Company’s future payments under the non-cancellable operating lease (in thousands): Year ending December 31, As of June 30, 2019 2019 (excluding the six months ended June 30, 2019) $ 237 2020 581 2021 598 2022 616 2023 526 Total undiscounted lease payments 2,558 Less: imputed interest (425 ) Total operating lease liabilities $ 2,133 Year ending December 31, As of December 31, 2018 2019 $ 564 2020 581 2021 598 2022 616 2023 526 Total payments $ 2,885 Legal Proceedings From time to time, the Company may become involved in legal proceedings arising from the ordinary course of its business. Management is currently not aware of any matters that could have a material adverse effect on the Company’s financial position, results of operations or cash flows. The Company records a legal liability when it believes that it is both probable that a liability may be imputed, and the amount of the liability can be reasonably estimated. Significant judgment by the Company is required to determine both probability and the estimated amount. Indemnification To the extent permitted under Delaware law, the Company has agreed to indemnify its directors and officers for certain events or occurrences while the director or officer is, or was serving, at the Company’s request in such capacity. The indemnification period covers all pertinent events and occurrences during the director’s or officer’s service. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is not specified in the agreements; however, the Company has director and officer insurance coverage that reduces its exposure and enables the Company to recover a portion of any future amounts paid. The Company believes the estimated fair value of these indemnification agreements in excess of applicable insurance coverage is minimal.

Stock-based Compensation

Stock-based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	7. Stock-based Compensation In January 2019, the number of shares of common stock available for issuance under the 2018 Equity Incentive Plan was increased by approximately 1.5 million shares as a result of the automatic increase provision in the 2018 Plan. Stock Options Stock option activity under the 2018 Plan and 2015 Equity Incentive Plan is summarized as follows (in thousands, except share and per share data). Outstanding Awards Number of Shares Available for Grant Number of Shares Underlying Outstanding Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Balance, December 31, 2018 3,024,404 5,135,267 $ 5.99 9.07 $ 10,681 Shares authorized 1,473,194 — Options exercised — (80,000 ) $ 1.04 290 Balance, March 31, 2019 4,497,598 5,055,267 $ 6.14 8.69 8,769 Options granted (449,988 ) 449,988 $ 8.40 Options forfeited or canceled 15,804 (15,804 ) $ 7.00 Options exercised — (21,284 ) $ 2.77 190 Balance, June 30, 2019 4,063,414 5,468,167 $ 6.34 8.60 $ 29,716 Stock-based compensation is classified in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 703 $ 312 $ 1,409 $ 365 General and administrative 541 345 992 384 Total stock-based compensation $ 1,244 $ 657 $ 2,401 $ 749 As of June 30, 2019, the unrecognized stock-based compensation of unvested employee options and unvested RSAs and RSUs was $14.9 million and it is expected to be recognized over a weighted-average period of 2.48 years.

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders	8. Net Loss per Share Attributable to Common Stockholders The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders which excludes shares which are legally outstanding, but subject to repurchase by the Company (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Numerator: Net loss attributable to common stockholders $ (11,385 ) $ (7,409 ) $ (19,369 ) $ (16,329 ) Denominator: Weighted-average common shares outstanding 37,314,540 7,946,102 37,295,858 7,941,430 Less: weighted-average unvested restricted shares and shares subject to repurchase (19,687 ) (189,021 ) (24,220 ) (220,463 ) Weighted-average common shares outstanding used in computing net loss per common share, basic and diluted 37,294,853 7,757,081 37,271,638 7,720,967 Net loss per share attributable to common stockholders, basic and diluted $ (0.31 ) $ (0.96 ) $ (0.52 ) $ (2.11 ) The following potentially dilutive securities, presented on an as-converted to common stock basis, were excluded from the computation of diluted net loss per share attributable to common stockholders for the period presented because including them would have been antidilutive: As of June 30, 2019 2018 Options to purchase common stock 5,468,167 3,383,478 Redeemable convertible preferred stock — 12,385,154 2017 convertible notes (1) — 2,497,722 2018 convertible notes (2) — 4,226,243 Redeemable convertible preferred stock warrants — 500,000 Unvested restricted stock awards 16,320 165,898 Unvested early exercised common stock options — 938 Total 5,484,487 23,159,433 (1) Calculated as $10.0 million in principal and $2.5 million in accrued but unpaid interest as of June 30, 2018, convertible at $5.00 per share of common stock. (2) Calculated as $33.0 million in principal and $0.8 million in accrued but unpaid interest as of June 30, 2018, convertible at 80% of the $10.00 per share of common stock from the Company’s IPO.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation and Principles of Consolidation The accompanying condensed consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) applicable to interim periods and, in the opinion of management, include all normal and recurring adjustments which are necessary to present fairly the Company's financial position and results of operations for the reported periods. The accompanying condensed consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities as of the date of the condensed consolidated financial statements and expenses during the reporting period. Actual results could differ from those estimates.
Leases	Leases The Company determines if an arrangement is, or contains, a lease at inception and then classifies the lease as operating or financing based on the underlying terms and conditions of the contract. Leases with terms greater than one year are initially recognized on the balance sheet as right-of-use assets and lease liabilities based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the incremental borrowing rate, which is the rate incurred to borrow, on a collateralized basis, an amount equal to the lease payments over a similar term and in a similar economic environment. The Company has elected not to recognize leases with terms of one year or less on the balance sheet.
Marketable Securities	Marketable Securities The Company invests excess cash balances in short-term marketable securities. The investments in marketable securities are classified as either held-to-maturity or available-for-sale based on facts and circumstances present at the time of purchase. Debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expensed over the life of the instrument. Equity securities with readily determinable fair values are also carried at fair value with unrealized gains and losses included in other income (expense), net. Realized gains and losses on both debt and equity securities are determined using the specific identification method and are included in other income (expense), net. If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary” and, if so, marks the investment to market through a charge to the Company’s statement of operations and comprehensive loss.
Recent Accounting Pronouncements	Recent a p From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) ASC Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Leases (Topic 842), Codification Improvements Leases (Topic 842), Targeted Improvements Leases The Company adopted the new lease standards as of January 1, 2019 using the modified retrospective approach to recognize a cumulative-effect adjustment on the effective date and to not adjust financial information and disclosures required under the new lease standards for comparative prior periods. The Company did not elect for the package of practical expedients and assessed all contracts at the transition date. The Company did not utilize the practical expedient which allows the use of hindsight in determining lease term and assessing impairment in right-of-use assets. The Company elected to apply the practical expedient and accounted for each lease component and related non-lease component as one single component. The Company elected not to recognize leases with terms of one year or less on the balance sheet. The adoption of the new lease standards on January 1, 2019 resulted in the initial recognition of right-of-use asset of $2.2 million and operating lease liability of $2.3 million related to the operating lease for the Company’s office and laboratory space in Palo Alto, California on the consolidated balance sheets with no material impact to the consolidated statements of operations, stockholders’ equity or cash flows. Refer to Note 6. In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260) Distinguishing Liabilities from Equity (Topic 480) Derivatives and Hedging (Topic 815) (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception The Company adopted this new guidance as of January 1, 2019, which did not result in a material impact on its 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 The Company adopted this new guidance as of January 1, 2019, which did not result in a material impact on its consolidated financial statements and related disclosures. New Accounting Pronouncements Not Yet Adopted Financial Instruments - Credit Losses (Topic 362): Measurement of Credit Losses on Financial Statements which intends to improve financial reporting by requiring earlier recognition of credit losses on certain financial assets, such as available-for-sale debt securities. The standard is effective for interim and annual periods after December 15, 2019. In August 2018, the FASB issued ASU 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurements In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract,

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2019
Accounts Payable And Accrued Liabilities Current [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): June 30, 2019 December 31, 2018 Accrued research and development $ 1,524 $ 1,387 Accrued salaries and benefits 1,425 2,061 Accrued legal fees 146 82 Accrued professional fees 46 117 Accrued other liabilities 136 129 Total accrued and other current liabilities $ 3,277 $ 3,776

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Summary of Fair Value Hierarchy for Assets Measured at Fair Value on Recurring Basis	The following tables present the Company’s fair value hierarchy for assets measured at fair value on a recurring basis (in thousands): Fair Value Measurements at June 30, 2019 Quoted Price in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Cash equivalents: Money market funds $ 44,785 $ — $ — $ 44,785 Marketable securities: Commercial paper — 13,082 — 13,082 Corporate notes — 10,052 — 10,052 Total $ 44,785 $ 23,134 $ — $ 67,919 Fair Value Measurements at December 31, 2018 Quoted Price in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Cash equivalents: Money market funds $ 87,957 $ — $ — $ 87,957 Total $ 87,957 $ — $ — $ 87,957

Marketable Securities (Tables)

Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2019
Investments Debt And Equity Securities [Abstract]
Summary of Marketable Securities Held	The following table summarizes the marketable securities held at June 30, 2019 (in thousands): Amortized Cost Unrealized Gains Unrealized Losses Fair Value Commercial paper $ 13,082 $ — $ — $ 13,082 Corporate notes 10,040 12 — 10,052 Total $ 23,122 $ 12 $ — $ 23,134

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Payments Under Non-Cancelable Operating Lease	The following tables summarize the Company’s future payments under the non-cancellable operating lease (in thousands): Year ending December 31, As of June 30, 2019 2019 (excluding the six months ended June 30, 2019) $ 237 2020 581 2021 598 2022 616 2023 526 Total undiscounted lease payments 2,558 Less: imputed interest (425 ) Total operating lease liabilities $ 2,133 Year ending December 31, As of December 31, 2018 2019 $ 564 2020 581 2021 598 2022 616 2023 526 Total payments $ 2,885

Stock-based Compensation (Table

Stock-based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Options Activity under 2018 Plan and 2015 Equity Incentive Plan	Stock option activity under the 2018 Plan and 2015 Equity Incentive Plan is summarized as follows (in thousands, except share and per share data). Outstanding Awards Number of Shares Available for Grant Number of Shares Underlying Outstanding Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Balance, December 31, 2018 3,024,404 5,135,267 $ 5.99 9.07 $ 10,681 Shares authorized 1,473,194 — Options exercised — (80,000 ) $ 1.04 290 Balance, March 31, 2019 4,497,598 5,055,267 $ 6.14 8.69 8,769 Options granted (449,988 ) 449,988 $ 8.40 Options forfeited or canceled 15,804 (15,804 ) $ 7.00 Options exercised — (21,284 ) $ 2.77 190 Balance, June 30, 2019 4,063,414 5,468,167 $ 6.34 8.60 $ 29,716
Summary of Stock-based Compensation Classified in Condensed Consolidated Statements of Operations and Comprehensive Loss	Stock-based compensation is classified in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 703 $ 312 $ 1,409 $ 365 General and administrative 541 345 992 384 Total stock-based compensation $ 1,244 $ 657 $ 2,401 $ 749

Net Loss per Share Attributab_2

Net Loss per Share Attributable to Common Stockholders (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders which excludes shares which are legally outstanding, but subject to repurchase by the Company (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Numerator: Net loss attributable to common stockholders $ (11,385 ) $ (7,409 ) $ (19,369 ) $ (16,329 ) Denominator: Weighted-average common shares outstanding 37,314,540 7,946,102 37,295,858 7,941,430 Less: weighted-average unvested restricted shares and shares subject to repurchase (19,687 ) (189,021 ) (24,220 ) (220,463 ) Weighted-average common shares outstanding used in computing net loss per common share, basic and diluted 37,294,853 7,757,081 37,271,638 7,720,967 Net loss per share attributable to common stockholders, basic and diluted $ (0.31 ) $ (0.96 ) $ (0.52 ) $ (2.11 )
Summary of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss per Share	The following potentially dilutive securities, presented on an as-converted to common stock basis, were excluded from the computation of diluted net loss per share attributable to common stockholders for the period presented because including them would have been antidilutive: As of June 30, 2019 2018 Options to purchase common stock 5,468,167 3,383,478 Redeemable convertible preferred stock — 12,385,154 2017 convertible notes (1) — 2,497,722 2018 convertible notes (2) — 4,226,243 Redeemable convertible preferred stock warrants — 500,000 Unvested restricted stock awards 16,320 165,898 Unvested early exercised common stock options — 938 Total 5,484,487 23,159,433 (1) Calculated as $10.0 million in principal and $2.5 million in accrued but unpaid interest as of June 30, 2018, convertible at $5.00 per share of common stock. (2) Calculated as $33.0 million in principal and $0.8 million in accrued but unpaid interest as of June 30, 2018, convertible at 80% of the $10.00 per share of common stock from the Company’s IPO.

The Company - Additional Inform

The Company - Additional Information (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (130,135)	$ (110,766)
Cash and cash equivalents and marketable securities	$ 68,100

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Operating lease right-of-use asset	$ 1,981
Operating lease liability	$ 2,133
Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Operating lease right-of-use asset		$ 2,200
Operating lease liability		$ 2,300

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accounts Payable And Accrued Liabilities Current [Abstract]
Accrued research and development	$ 1,524	$ 1,387
Accrued salaries and benefits	1,425	2,061
Accrued legal fees	146	82
Accrued professional fees	46	117
Accrued other liabilities	136	129
Total accrued and other current liabilities	$ 3,277	$ 3,776

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Fair Value Hierarchy for Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	$ 23,134
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	67,919	$ 87,957
Fair Value, Measurements, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	44,785	87,957
Fair Value, Measurements, Recurring | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	13,082
Fair Value, Measurements, Recurring | Corporate Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	10,052
Quoted Price in Active Markets (Level 1) | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	44,785	87,957
Quoted Price in Active Markets (Level 1) | Fair Value, Measurements, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	44,785	87,957
Quoted Price in Active Markets (Level 1) | Fair Value, Measurements, Recurring | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0
Quoted Price in Active Markets (Level 1) | Fair Value, Measurements, Recurring | Corporate Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0
Significant Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	23,134	0
Significant Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Significant Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	13,082
Significant Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	10,052
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	$ 0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Corporate Notes
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	$ 0

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities Held (Details) $ in Thousands	Jun. 30, 2019USD ($)
Marketable Securities [Line Items]
Amortized Cost	$ 23,122
Unrealized Gains	12
Fair Value	23,134
Commercial Paper
Marketable Securities [Line Items]
Amortized Cost	13,082
Fair Value	13,082
Corporate Notes
Marketable Securities [Line Items]
Amortized Cost	10,040
Unrealized Gains	12
Fair Value	$ 10,052

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)
Marketable Securities [Line Items]
Realized gains or losses recognized on sale or maturity of available-for-sale debt securities	$ 0
Impairment charges related to marketable securities	$ 0
Maximum
Marketable Securities [Line Items]
Marketable securities, contractual maturities	1 year

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
Estimated incremental borrowing rate used to determine discounted present value of remaining lease payments	8.50%	8.50%
Remaining operating lease term	4 years 9 months 29 days	4 years 9 months 29 days
Operating lease cost	$ 0.1	$ 0.3
Operating cash flows used for operating leases		$ 0.3

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Future Payments Under Non-Cancelable Operating Lease (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Operating Lease
2019 (excluding the six months ended June 30, 2019)	$ 237
2020	581
2021	598
2022	616
2023	526
Total undiscounted lease payments	2,558
Less: imputed interest	(425)
Total operating lease liabilities	$ 2,133
Operating Lease
2019		$ 564
2020		581
2021		598
2022		616
2023		526
Total payments		$ 2,885

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($) shares in Millions, $ in Millions	1 Months Ended	6 Months Ended
	Jan. 31, 2019	Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation of unvested employee options and unvested RSAs and RSUs		$ 14.9
Unrecognized stock-based compensation of unvested stock awards, weighted-average period expected for recognition		2 years 5 months 23 days
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock available for issuance increased	1.5

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Options Activity under 2018 Plan and 2015 Equity Incentive Plan (Details) - 2018 Plan and 2015 Equity Incentive Plan - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Number of Shares Available for Grant
Beginning balance	4,497,598	3,024,404
Shares authorized		1,473,194
Options granted	(449,988)
Options forfeited or canceled	15,804
Ending balance	4,063,414	4,497,598	3,024,404
Number of Shares Underlying Outstanding Options
Beginning balance	5,055,267	5,135,267
Options granted	449,988
Options forfeited or canceled	(15,804)
Options exercised	(21,284)	(80,000)
Ending balance	5,468,167	5,055,267	5,135,267
Weighted Average Exercise Price
Beginning balance	$ 6.14	$ 5.99
Options granted	8.40
Options forfeited or canceled	7
Options exercised	2.77	1.04
Ending balance	$ 6.34	$ 6.14	$ 5.99
Weighted Average Remaining Contractual Term (in years)
Weighted Average Remaining Contractual Term (in years)	8 years 8 months 8 days	8 years 8 months 8 days	9 years 25 days
Aggregate Intrinsic Value
Beginning balance	$ 8,769	$ 10,681
Options exercised	190	290
Ending balance	$ 29,716	$ 8,769	$ 10,681

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Stock-based Compensation Classified in Condensed Consolidated Statements of Operations and Comprehensive Loss (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]
Total stock-based compensation	$ 1,244	$ 657	$ 2,401	$ 749
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	703	312	1,409	365
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 541	$ 345	$ 992	$ 384

Net Loss per Share Attributab_3

Net Loss per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net loss attributable to common stockholders	$ (11,385)	$ (7,984)	$ (7,409)	$ (8,920)	$ (19,369)	$ (16,329)
Denominator:
Weighted-average common shares outstanding	37,314,540		7,946,102		37,295,858	7,941,430
Less: weighted-average unvested restricted shares and shares subject to repurchase	(19,687)		(189,021)		(24,220)	(220,463)
Weighted-average common shares outstanding used in computing net loss per common share, basic and diluted	37,294,853		7,757,081		37,271,638	7,720,967
Net loss per share attributable to common stockholders, basic and diluted	$ (0.31)		$ (0.96)		$ (0.52)	$ (2.11)

Net Loss per Share Attributab_4

Net Loss per Share Attributable to Common Stockholders - Summary of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss per Share (Details) - shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	5,484,487	23,159,433
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	5,468,167	3,383,478
2017 Convertible Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	0	2,497,722
2018 Convertible Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	0	4,226,243
Redeemable Convertible Preferred Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	0	500,000
Unvested Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	16,320	165,898
Unvested Early Exercised Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	0	938
Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	0	12,385,154

Net Loss per Share Attributab_5

Net Loss per Share Attributable to Common Stockholders - Summary of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss per Share (Parenthetical) (Details) $ / shares in Units, $ in Millions	Jun. 30, 2018USD ($)$ / shares
2017 Convertible Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Convertible notes, principal amount	$ 10
Convertible notes, accrued but unpaid interest	$ 2.5
Convertible notes, conversion price per share of common stock | $ / shares	$ 5
2018 Convertible Notes | Initial Public Offering
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Convertible notes, principal amount	$ 33
Convertible notes, accrued but unpaid interest	$ 0.8
Percentage of initial public offering per share price	80.00%
2018 Convertible Notes | Initial Public Offering | Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Convertible notes, conversion price per share of common stock | $ / shares	$ 10