0001564590-21-043101 | 10-Q | XBRL Viewer

Term Loan Facility

6 Months Ended

Jun. 30, 2021

7. Term Loan Facility

On August 3, 2020, the Company entered into a Loan and Security Agreement (the “Loan Agreement”) with Hercules Capital, Inc. (“Hercules”). Under the Loan Agreement, Hercules provided the Company with access to a term loan with an aggregate principal amount of up to $80.0 million (the “Term Loan Facility”), available in four tranches, subject to certain terms and conditions. The first tranche of $25.0 million was advanced to the Company on the date the Loan Agreement was executed. The milestones for the remaining tranches have not yet been reached and as of June 30, 2021 are not expected to be reached as they were dependent, in whole or in part, upon continued advancement in the clinical development of UBX0101 in patients with osteoarthritis of the knee. The Company expects to make interest only payments through September 1, 2022 and expects to then repay the principal balance and interest in equal monthly installments through August 1, 2024.

The Company may prepay advances under the Loan Agreement, in whole or in part, at any time subject to a prepayment charge of up to 1.50% of any amount prepaid, depending upon when the prepayment occurs. Upon prepayment or repayment of all or any of the term loans under the Term Loan Facility, the Company is required to pay an end of term fee (“End of Term Fee”) equal to 6.25% of the total aggregate amount of the term loans being prepaid or repaid, which has been recorded as a discount on the principal balance upon issuance.

Interest on the term loan accrues at a per annum rate equal to the greater of (i) the Wall Street Journal prime rate plus 6.10% and (ii) 9.35%. On June 30, 2021, the rate was 9.35 %. Interest expense is calculated using the effective interest method and is inclusive of non-cash amortization of capitalized loan issuance costs. At June 30, 2021, the effective interest rate was 12.40%.

Under the terms of the Loan Agreement, the Company granted first priority liens and security interests in substantially all of the Company’s intellectual property as collateral for the obligations thereunder. The Company also granted Hercules the right, at their discretion, to participate in any closing of any single subsequent financing as defined up to a maximum aggregate amount of $2.0 million. The Loan Agreement also contains representations and warranties by the Company and Hercules, indemnification provisions in favor of Hercules and customary affirmative and negative covenants (including a liquidity covenant beginning July 1, 2021, requiring the Company to maintain at least $15.0 million in unrestricted cash), and events of default, including a material adverse change in the Company’s business, payment defaults, breaches of covenants following any applicable cure period, and a material impairment in the perfection or priority of Hercules’ security interest in the collateral. In the event of default by the Company under the Loan Agreement, the Company may be required to repay all amounts then outstanding under the Loan Agreement. As of June 30, 2021, the Company was in compliance with all covenants under the Loan Agreement.

As of June 30, 2021, the carrying value of the term loan consists of $25.0 million principal outstanding less the debt discount and issuance costs of approximately $1.7 million. The End of Term Fee of $1.6 million is recognized over the life of the term loan as interest expense using the effective interest method. The debt issuance costs have been recorded as a debt discount which are being accreted to interest expense through the maturity date of the term loan.

Interest expense relating to the term loan, which is included in interest expense in the condensed statements of operations and comprehensive loss, was $0.8 million and $1.6 million for the three and six months ended June 30, 2021, respectively. There was no interest expense for the three and six months ended June 30, 2020.

Future principal payments for the long-term debt are as follows (in thousands):

	June 30, 2021
2021 (for the remaining 6 months)	$	—
2022		3,838
2023		12,272
2024		8,890
Total principal payments		25,000
End of term fee due at maturity in 2024		1,562
Total principal and end of term fee payments		26,562
Unamortized discount and debt issuance costs		(1,670	)
Long-term debt, net	$	24,892

Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2021

Investments Debt And Equity Securities [Abstract]

Summary of Marketable Securities Classified as Available-for-Sale

Marketable securities, which are classified as available-for-sale, consisted of the following as of June 30, 2021 (in thousands):

	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	$	9,498	$	—	$	—		$	9,498
Total cash equivalents		9,498		—		—			9,498
Short-term marketable securities:
U.S. government debt securities		9,035		2		—			9,037
U.S. treasuries		61,401		8		(1	)		61,408
Total short-term marketable securities		70,436		10		(1	)		70,445
Long-term marketable securities:
U.S. treasuries		11,502		—		(5	)		11,497
U.S. government debt securities		2,044		1		—			2,045
Total long-term marketable securities		13,546		1		(5	)		13,542
Total	$	93,480	$	11	$	(6	)	$	93,485

Marketable securities, which are classified as available-for-sale, consisted of the following as of December 31, 2020 (in thousands):

	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	$	13,686	$	—	$	—		$	13,686
Total cash equivalents		13,686		—		—			13,686
Short-term marketable securities:
U.S. and foreign commercial paper		11,998		1		—			11,999
U.S. and foreign corporate debt securities		1,001		—		—			1,001
U.S. government debt securities		11,541		2		—			11,543
U.S. treasuries		55,350		2		(3	)		55,349
Total short-term marketable securities		79,890		5		(3	)		79,892
Long-term marketable securities
U.S. treasuries		7,369		1		—			7,370
U.S. government debt securities		10,498		3		—			10,501
Total long-term marketable securities		17,867		4		—			17,871
Total	$	111,443	$	9	$	(3	)	$	111,449

Commitments and Contingencies (Tables)

6 Months Ended

Jun. 30, 2021

Commitments And Contingencies Disclosure [Abstract]

Summary of Components of Lease Expense

The following table summarizes the components of lease expense, which are included in operating expenses in the Company’s condensed statements of operations and comprehensive loss (in thousands):

	Three Months Ended June 30,					Six Months Ended June 30,
	2021			2020		2021			2020
Operating lease cost	$	1,091		$	1,144	$	2,187		$	2,444
Variable lease cost		387			363		853			641
Sublease income		(390	)		—		(535	)		—
Impairment of operating lease right-of-use asset		—			—		—			1,157
Total lease cost	$	1,088		$	1,507	$	2,505		$	4,242

Summary of Supplemental Information Related to Leases

The following table summarizes supplemental information related to leases (in thousands):

	Six Months Ended June 30,
	2021			2020
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$	3,313		$	2,557
Weighted-average remaining lease term (years)
Operating leases		8.1			8.8
Weighted-average discount rate (percentage)
Operating leases		5.9	%		5.8	%

Summary of Maturities of Lease Liabilities

The following table summarizes the maturities of lease liabilities as of June 30, 2021 (in thousands):

	Amount
2021 (remaining 6 months)	$	3,343
2022		6,283
2023		4,810
2024		4,964
2025		5,123
Thereafter		22,179
Total future minimum lease payments		46,702
Less: Amount representing interest		(9,930	)
Present value of future minimum lease payments		36,772
Less: Current portion of operating lease liability		(4,736	)
Noncurrent portion of operating lease liability	$	32,036

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities
Net loss	$ (33,582)	$ (46,705)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,501	1,814
Amortization of debt issuance costs	384	0
Net accretion and amortization of premium and discounts on marketable securities	603	(54)
Stock-based compensation	5,526	7,421
Non-cash rent expense	(1,124)	(106)
Impairment of long-lived assets	0	2,159
Change in fair value of strategic investment	0	(3,060)
Change in fair value of contingent consideration	0	685
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(498)	(2,002)
Other long-term assets	0	29
Accounts payable	(696)	(1,262)
Accrued compensation	(2,742)	(2,271)
Accrued liabilities and other current liabilities	2,130	(1,005)
Other long-term liabilities	23	0
Net cash used in operating activities	(28,475)	(44,357)
Investing activities
Purchase of marketable securities	(56,577)	(49,792)
Maturities of marketable securities	69,750	65,345
Realized gain on sale of strategic investments	0	799
Purchase of property and equipment	(90)	(377)
Net cash provided by investing activities	13,083	15,975
Financing activities
Proceeds from issuance of common stock under ATM offering program, net of issuance costs	8,893	29,494
Proceeds from issuance of common stock upon exercise of stock options, net of repurchases	1,784	0
Proceeds from issuance of common stock under equity incentive plans, net of repurchases	0	604
Proceeds from repayment of recourse notes	210	56
Proceeds from issuance of common stock under 2018 ESPP	196	385
Payments made on capital lease obligations	0	(38)
Net cash provided by financing activities	11,083	30,501
Net increase (decrease) in cash, cash equivalents and restricted cash	(4,309)	2,119
Cash, cash equivalents and restricted cash at beginning of the period	19,253	38,919
Cash, cash equivalents and restricted cash at end of the period	14,944	41,038
Supplemental Disclosures of Cash Flow Information:
Cash paid for interest	1,182	0
Supplemental Disclosures of Non-Cash Investing and Financing Activities
Property and equipment included in accounts payable and accrued liabilities	36	30
Issuance of shares in settlement of share-based liability	$ 0	$ 100

Fair Value Measurements

6 Months Ended

Jun. 30, 2021

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company determines the fair value of financial and non-financial assets and liabilities based on the assumptions that market participants would use in pricing the asset or liability in an orderly transaction between market participants at the measurement date. The identification of market participant assumptions provides a basis for determining what inputs are to be used for pricing each asset or liability. A fair value hierarchy has been established which gives precedence to fair value measurements calculated using observable inputs over those using unobservable inputs. This hierarchy prioritized the inputs into three broad levels as follows:

•

Level 1: Quoted prices in active markets for identical instruments

•

Level 2: Other significant observable inputs (including quoted prices in active markets for similar instruments)

•

Level 3: Significant unobservable inputs (including assumptions in determining the fair value of certain investments)

The carrying amounts of financial instruments such as cash and cash equivalents, restricted cash, prepaid expenses and other current assets, accounts payable, accrued compensation, accrued and other current liabilities approximate the related fair values due to the short maturities of these instruments. As the long-term debt is subject to variable

interest rates that are based on market rates which are regularly reset, considering level 2 inputs, the Company believes the carrying value of the long-term debt approximates its fair value.

The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements were as follows (in thousands):

	June 30, 2021
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	9,498	$	9,498	$	—	$	—
Total cash equivalents		9,498		9,498		—		—
Short-term marketable securities:
U.S. government debt securities		9,037		—		9,037		—
U.S. treasuries		61,408		—		61,408		—
Total short-term marketable securities		70,445		—		70,445		—
Long-term marketable securities:
U.S. treasuries		11,497		—		11,497		—
U.S. government debt securities		2,045		—		2,045		—
Total long-term marketable securities		13,542		—		13,542		—
Total assets subject to fair value measurements on a recurring basis	$	93,485	$	9,498	$	83,987	$	—

	December 31, 2020
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	13,686	$	13,686	$	—	$	—
Total cash equivalents		13,686		13,686		—		—
Short-term marketable securities:
U.S. treasuries		55,349		—		55,349		—
U.S. and foreign commercial paper		11,999		—		11,999		—
U.S. and foreign corporate debt securities		1,001		—		1,001		—
U.S. government debt securities		11,543		—		11,543		—
Total short-term marketable securities		79,892		—		79,892		—
Long-term marketable securities:
U.S. treasuries		7,370		—		7,370		—
U.S. government debt securities		10,501		—		10,501		—
Total long-term marketable securities		17,871		—		17,871		—
Total assets subject to fair value measurements on a recurring basis	$	111,449	$	13,686	$	97,763	$	—

The Company estimates the fair value of its money market funds, U.S. and foreign commercial paper, U.S. and foreign corporate debt securities, U.S. treasuries, and U.S. government debt securities by taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads; benchmark securities; prepayment/default projections based on historical data; and other observable inputs. See Note 4, “Marketable Securities,” for further information regarding the carrying value of the Company's financial instruments.

The Company had previously recorded a contingent consideration liability related to three agreements (the “Commercial Agreements”) with Ascentage Pharma Group Corp. Limited, a clinical-stage biopharmaceutical company based in Hong Kong China (“Ascentage Pharma”). See Note 5, “License Agreements and Strategic

Investment”. The fair value of the contingent consideration liability at December 31, 2019 included inputs not observable in the market and thus represented a Level 3 measurement. The probability of achieving the defined milestone events under the Commercial Agreements was estimated on a quarterly basis by the Company’s management using a probability-weighted valuation approach model which utilized current stock price and reflected the probability and timing of future issuances of shares. As a result of settlements and changes made to the Commercial Agreements, there was no contingent consideration liability at June 30, 2021 and December 31, 2020.

The following table provides a reconciliation of the Company’s financial liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) at June 30, 2020 (in thousands):

	Amount
Balance at December 31, 2019	$	1,131
Additions		—
Settlements		—
Change in fair value		685
Balance at June 30, 2020	$	1,816

There were no transfers into and out of Level 3 of the fair value hierarchy during the six months ended June 30, 2021 and 2020.

- 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

Related-Party Transactions - Additional Information (Details) - Non-executive Officer - Promissory Note - USD ($) $ in Thousands	1 Months Ended
	Dec. 31, 2019	Jan. 31, 2018	Jun. 30, 2021	Mar. 31, 2021
Related Party Transaction [Line Items]
Due from related parties	$ 200	$ 200
Promissory notes for purchase of common stock			$ 0	$ 200
Interest rate	1.51%	2.50%
Common Stock
Related Party Transaction [Line Items]
Early exercise options in aggregate		59,322

Condensed Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	10,000,000	10,000,000
Convertible preferred stock, shares issued	0	0
Convertible preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	55,104,250	53,253,213
Common stock, shares outstanding	55,104,250	53,253,213

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Cash and cash equivalents	$ 13,498	$ 17,807
Restricted cash	1,446	1,446
Total cash, cash equivalents, and restricted cash	$ 14,944	$ 19,253	$ 41,038	$ 38,919

Net Loss per Common Share - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($) d shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Milestone Payments \| $	$ 2.0
Common stock determination threshold trading days	20
Days for common stock issue on milestone achievement	60
Maximum
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares contingently issued \| shares	89,900

Marketable Securities - Summary of Marketable Securities Classified as Available-for-Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 93,480	$ 111,443
Unrealized Gains	11	9
Unrealized Losses	(6)	(3)
Fair Value	93,485	111,449
Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	9,498	13,686
Fair Value	9,498	13,686
Cash Equivalents \| Money market funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	9,498	13,686
Fair Value	9,498	13,686
Short Term Marketable Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	70,436	79,890
Unrealized Gains	10	5
Unrealized Losses	(1)	(3)
Fair Value	70,445	79,892
Short Term Marketable Securities \| U.S. government debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	9,035	11,541
Unrealized Gains	2	2
Fair Value	9,037	11,543
Short Term Marketable Securities \| U S Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	61,401	55,350
Unrealized Gains	8	2
Unrealized Losses	(1)	(3)
Fair Value	61,408	55,349
Short Term Marketable Securities \| U.S. and foreign commercial paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis		11,998
Unrealized Gains		1
Fair Value		11,999
Short Term Marketable Securities \| U.S. and foreign corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis		1,001
Fair Value		1,001
Long Term Marketable Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	13,546	17,867
Unrealized Gains	1	4
Unrealized Losses	(5)
Fair Value	13,542	17,871
Long Term Marketable Securities \| U.S. government debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	2,044	10,498
Unrealized Gains	1	3
Fair Value	2,045	10,501
Long Term Marketable Securities \| U S Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	11,502	7,369
Unrealized Gains		1
Unrealized Losses	(5)
Fair Value	$ 11,497	$ 7,370

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2021

Accounting Policies [Abstract]

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the balance sheets that sum to the total of the same amounts shown in the condensed statements of cash flows (in thousands).

	June 30, 2021		December 31, 2020
Cash and cash equivalents	$	13,498	$	17,807
Restricted cash		1,446		1,446
Total cash, cash equivalents, and restricted cash	$	14,944	$	19,253

Net Loss per Common Share

6 Months Ended

Jun. 30, 2021

Earnings Per Share [Abstract]

Net Loss per Common Share

12. Net Loss per Common Share

Basic net loss per share is calculated by dividing net loss by the weighted-average number of shares outstanding for the period. Diluted net loss per share is calculated by dividing net loss by the weighted-average number of shares of common stock and potential dilutive common stock equivalents outstanding during the period if the effect is dilutive.

The calculation of diluted earnings (loss) per share also requires that, to the extent contingencies are satisfied during the period and the presumed issuance of additional shares as contingent consideration is dilutive to earnings (loss) per share for the period, adjustments to net income or net loss used in the calculation are required to remove the change in fair value of the contingent consideration liability for the period. Likewise, adjustments to the denominator are required to reflect the related dilutive shares. In all periods presented, the Company’s outstanding stock options, RSUs (including PSUs), early exercised common stock subject to future vesting, restricted stock accounted for as options, shares subject to the 2018 ESPP and presumed issuance of additional shares as contingent consideration were excluded from the calculation of diluted net loss per share because their effects were antidilutive.

A reconciliation of the numerators and denominators used in computing net loss from continuing operations per share is as follows (in thousands, except share and per share amounts):

	Three Months Ended June 30,						Six Months Ended June 30,
	2021			2020			2021			2020
Numerator:
Net loss	$	(17,826	)	$	(18,667	)	$	(33,582	)	$	(46,705	)
Denominator:
Weighted-average number of shares outstanding—basic and diluted		54,859,727			49,659,153			54,516,445			48,606,768
Net loss per share—basic and diluted	$	(0.32	)	$	(0.38	)	$	(0.62	)	$	(0.96	)

Since the Company was in a net loss position for all periods presented, basic net loss per common share is the same as diluted net loss per common share as the inclusion of all potential common shares outstanding would have been anti-dilutive.

Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:

	June 30,
	2021		2020
Options to purchase common stock		8,625,251		9,468,522
Early exercised common stock subject to future vesting		33,370		80,285
RSUs		2,990,123		840,642
Shares subject to 2018 ESPP		80,778		68,188
Total		11,729,522		10,457,637

Upon the dosing of the first patient in the Phase 2a UBX1325 study in June 2021, a milestone payment of $2.0 million to Ascentage Pharma was triggered. The liability will be settled in shares of the Company’s common stock. The number of shares will be determined based on the fixed dollar amount and the 20 days average trading price prior to the issuance date. The Company has up to 60 days from the date of achievement of the milestone to issue the shares. The issuance of the shares would be anti-dilutive for the three and six months ended June 30, 2021, and therefore, these shares have not been included in the calculation of dilutive net loss per share.

Up to 89,900 shares may be contingently issued, if certain performance conditions are met under the Company’s in-licensing agreements. See Note 5, “License Agreements and Strategic Investments,” to our condensed financial statements for additional information.

License Agreements and Strategic Investment

6 Months Ended

Jun. 30, 2021

License Agreements And Strategic Investment [Abstract]

License Agreements and Strategic Investment

5. License Agreements and Strategic Investment

License and Compound Library and Option Agreement

The Company is a party to three agreements, two active and one terminated, with Ascentage Pharma: (a) a compound library and option agreement executed in February 2016 granting the Company the right to identify and take licenses to research, develop, and seek and obtain marketing approval for library compounds for the treatment of indications outside of oncology (the “Library Agreement”), (b) an initial license agreement executed in February 2016 granting the Company rights to an initial Ascentage Pharma compound known as APG1252 (the “APG1252 License Agreement”), and (c) a second license agreement executed in January 2019 granting the Company rights to a second licensed compound (this second license agreement, the “Bcl License Agreement” and collectively with the Library Agreement and APG1252 License Agreement, the “Commercial Agreements”). On July 30, 2020, the Company notified Ascentage Pharma of its termination of the APG1252 License Agreement due to the Company’s decision to prioritize the progression of other compounds from Ascentage International’s library of Bcl-2 inhibitors, such as UBX1325, a Bcl-xL inhibitor.

The Commercial Agreements referenced above include cash payments of up to $70.3 million as well as the equity payments of up to an aggregate of (a) 933,337 shares of common stock in the event there is only one licensed product, and (b) 1,333,338 shares of common stock in the event there are two or more licensed products, in each case to be issued based on the Company’s achievement of certain preclinical and clinical development and sales milestone events. The Company is required to make 80% of all equity payments to Ascentage Pharma and the remaining 20% to an academic institution from whom Ascentage Pharma had previously licensed the technology. The milestones include the advancement of additional compounds into Investigational New Drug application (“IND”) enabling studies, the filing of an IND, the commencement of clinical studies, Food and Drug Administration (“FDA”) and/or European Medicines Agency approval, and a net sales threshold. The Bcl License Agreement also includes tiered royalties in the low-single digits based on sales of licensed products.

As of June 30, 2021, pursuant to these agreements, the Company had issued 974,980 shares of common stock to Ascentage Pharma and 186,667 shares of common stock to the academic institution from whom Ascentage Pharma had previously licensed the technology. In May 2021, the Company initiated a Phase 2a proof-of-concept study of UBX1325 in patients with diabetic macular edema. As a result of the first patient dosed in the Phase 2a UBX1325 study in June 2021, the Company triggered a milestone payment of $2.0 million for Ascentage Pharma. The Company has elected to settle in shares of the Company’s common stock, which will be determined based on the fixed dollar amount. These shares will be issued in the three months ended September 30, 2021. The milestone payment is accrued and recognized as research and development expense in the statement of operations and comprehensive loss during the three months ended June 30, 2021.

The Commercial Agreements included contingent consideration in the form of additional issuances of shares of the Company’s common stock based on the achievement of the specified milestones. Upon the July 2020 termination of the license to APG1252, the Company determined that the contingency no longer applied and adjusted the fair value of the contingent consideration liability to zero. To date, no royalties were due from the sales of licensed products.

Strategic Investment

The Company previously held an equity investment in Ascentage International, an affiliate of Ascentage Pharma. The equity interest represented an insignificant level of ownership in the investee and was recorded within strategic investment on the Company’s condensed balance sheets. The fair value of the Company’s equity investment in Ascentage International was zero as of June 30, 2021 and December 31, 2020. The change in fair value of this investment was $4.4 million and $3.1 million for the three and six months ended June 30, 2020, respectively, and was recorded in other expense on the condensed statements of operations and comprehensive loss.

The Company agreed to provide funding to Ascentage Pharma for research and development work performed at a cost of up to $2.0 million through February 2020. During the period ended June 30, 2020, the research and development expense under the research services agreement was not material to the Company’s financial statements.

Other License Agreements with Research Institutions

In May 2019, the Company entered into an exclusive license agreement with The Regents of the University of California on behalf of its San Francisco campus (collectively, “UCSF”) which provides the Company the rights to certain patents and related know-how to make, use, sell, offer for sale, and import certain products and practice certain methods for use in the development of human therapeutics, which excludes the provision of services to third parties for consideration of any kind. The license to the Company is subject to UCSF’s reserved rights under the licensed intellectual property for educational and non-commercial research purposes and a requirement to substantially manufacture any licensed products in the United States. The Company is obligated to use diligent efforts to develop and obtain regulatory approval for at least one product commercialized pursuant to the agreement and must meet certain regulatory and development milestones. In June 2019, as part of this license agreement, the Company issued 120,000 shares of its common stock to UCSF. In addition, the Company is obligated to pay an annual license maintenance fee except in years in which the Company is responsible for royalties to UCSF and may be obligated to make milestone payments or issue up to an additional 34,000 shares of its common stock upon the occurrence of specified development events, up to aggregate milestone payments of $13.6 million for each product licensed under the agreement, and upon commercialization, to make royalty payments in the low single digit percentages (subject to a specified minimum annual royalty) based on the type of Licensed Product commercialized pursuant to the agreement. None of these events had occurred and no milestone payments or royalty payments had been recognized as of June 30, 2021. The upfront issuance of 120,000 shares of the Company’s common stock was valued at $1.0 million and recorded as additional paid-in capital upon issuance in June 2019.

The Company has also entered into license agreements with various other research institutions which have provided the Company with rights to patents, and in certain cases, research “know-how” and proprietary research tools to research, develop and commercialize drug candidates. In addition to upfront consideration paid to these various research institutions in either cash or shares of the Company’s common stock, the Company may be obligated to pay milestone payments in cash or the issuance of the Company’s common stock upon achievement of certain specified clinical development and/or sales events. The contingent consideration liability considered to be a derivative associated with the potential issuance of common stock related to these license agreements was not probable at June 30, 2021 or December 31, 2020. To date, none of these events have occurred and no contingent consideration, milestone or royalty payments have been recognized.

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2021	Aug. 06, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Trading Symbol	UBX
Entity Registrant Name	Unity Biotechnology, Inc.
Entity Central Index Key	0001463361
Current Fiscal Year End Date	--12-31
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		55,104,250
Entity Shell Company	false
Entity File Number	001-38470
Entity Tax Identification Number	26-4726035
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	285 East Grand Ave.
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	416-1192
Title of 12(b) Security	Common Stock, par value $0.0001
Security Exchange Name	NASDAQ

Organization

6 Months Ended

Jun. 30, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization

1. Organization

Description of Business

Unity Biotechnology, Inc. (the “Company”) is a biotechnology company engaged in the research and development of therapeutics to slow, halt, or reverse diseases of aging. The Company devotes substantially all of its time and efforts to performing research and development, raising capital, and recruiting personnel. The Company’s headquarters are located in South San Francisco, California. The Company was incorporated in the State of Delaware in 2009.

Liquidity

The Company has incurred operating losses and has an accumulated deficit as a result of ongoing efforts to develop drug product candidates, including conducting preclinical and clinical trials and providing general and administrative support for these operations. The Company had an accumulated deficit of $372.9 million and $339.3 million as of June 30, 2021 and December 31, 2020, respectively. The Company had net losses of $17.8 million and $33.6 million for the three and six months ended June 30, 2021, respectively, net losses of $18.7 million and $46.7 million for the three and six months ended June 30, 2020, respectively, and net cash used in operating activities of $28.5 million and $44.4 million for the six months ended June 30, 2021 and 2020, respectively. To date, none of the Company’s drug candidates have been approved for sale, and therefore, the Company has not generated any revenue from contracts with customers and does not expect positive cash flows from operations in the foreseeable future. The Company has financed its operations primarily through private placements of preferred stock and promissory notes, public equity issuances and more recently, from its ATM Offering Programs (as defined below) and the Term Loan Facility (as defined below), and will continue to be dependent upon equity and/or debt financing until the Company is able to generate positive cash flows from its operations. See Note 7, “Term Loan Facility”.

The Company had cash, cash equivalents, and marketable securities of $97.5 million as of June 30, 2021. The Company has evaluated and concluded there are no conditions or events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern for a period of twelve (12) months following the date that these condensed financial statements are issued. Management expects operating losses to continue for the foreseeable future. As a result, the Company will need to raise additional capital. If sufficient funds on acceptable terms are not available when needed, the Company could be required to significantly reduce its operating expenses and delay, reduce the scope of, or eliminate one or more of its development programs. Failure to manage discretionary spending or raise additional financing, as needed, may adversely impact the Company’s ability to achieve its intended business objectives.

Stock-Based Compensation

6 Months Ended

Jun. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

11. Stock-Based Compensation

Stock Options and Restricted Stock Units Activity

A summary of the Company’s stock option activity under the 2013 Equity Incentive Plan, 2018 Incentive Award Plan, and 2020 Employment Inducement Incentive Plan for the six months ended June 30, 2021 is as follows:

	Number of Shares			Weighted- Average Exercise Price
Balances at December 31, 2020		7,475,472		$	6.88
Granted		2,638,838		$	5.23
Exercised		(430,047	)	$	3.64
Canceled		(1,059,012	)	$	9.09
Balances at June 30, 2021		8,625,251		$	6.27

A summary of the Company’s restricted stock units (“RSUs”), performance stock units (“PSUs”), and restricted stock awards (“RSAs”) activity for the six months ended June 30, 2021 is as follows:

	Number of Shares			Weighted- Average Grant Date Fair Value
Unvested at December 31, 2020		2,922,077		$	3.44
Granted		536,723		$	5.02
Vested		(111,297	)	$	6.58
Canceled		(357,380	)	$	3.35
Unvested at June 30, 2021		2,990,123		$	3.62

For stock options granted to employees with service-based vesting, the fair value of stock options granted to employees was estimated on the date of grant using the Black-Scholes option pricing model and utilizing assumptions that were determined as follows:

Expected Term—The expected term represents the period that the options granted are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term) as the Company has concluded that its stock option exercise history does not provide a reasonable basis upon which to estimate expected term.

Expected Volatility—Due to limited historical data, the Company estimates stock price volatility based on a combined weighted-average of the Company’s historical average volatility and that of a selected peer group of comparable publicly traded companies within the biotechnology and pharmaceutical industry that were deemed to be representative of future stock price trends over the expected life of the award.

Risk-Free Interest Rate—The Company based the risk-free interest rate over the expected term of the options based on the constant maturity rate of U.S. Treasury securities with similar maturities as of the date of the grant.

Expected Dividends—The Company has never paid any dividends and does not plan to pay dividends in the foreseeable future. Therefore, the expected dividend yield is zero.

In March 2020, the board of directors granted the Company’s newly hired Chief Executive Officer stock-based awards covering an aggregate of 1.1 million shares of common stock, including options to purchase an aggregate of 800,000 shares of common stock, 120,000 RSUs, 150,000 PSUs, and 30,000 shares of common stock. The stock-based awards were granted pursuant to the 2020 Employment Inducement Incentive Plan, which was approved by the board of directors in March 2020 to provide for grants to newly hired employees as a material inducement for them to commence employment with the Company.

The 30,000 shares of common stock were fully vested on the date of grant and thus, the related compensation expense of $0.2 million was recognized on the grant date. The stock options and RSUs will vest subject to continued service through the applicable vesting date.

The PSUs were originally scheduled to vest as to 50,000 PSUs upon the attainment of (a) a volume-weighted average per share closing trading price of the Company’s common stock of at least $36.875 over a trailing 30-day period or (b) a change in control transaction in which the price per share to the holders of the Company’s common stock is at least $36.875 and as to 100,000 PSUs (x) at such time as the Company’s market capitalization reaches at least $2.5 billion, as measured based on the volume weighted-average closing trading price over a trailing 30 day period or (y) a change in control transaction in which the consideration paid to the Company’s stockholders is equal to at least $2.5 billion, as determined by the Company’s board of directors. In January 2021, the board of directors modified the PSUs to vest as to 50,000 PSUs upon the attainment of (a) a volume-weighted average per share closing trading price of the Company’s common stock of at least $18 over a trailing 30-day period or (b) a change in control transaction in which the price per share to the holders of the Company’s common stock is at least $18.00 and as to 100,000 PSUs upon the attainment of (x) a volume-weighted average per share closing trading price of the Company’s common stock of at least $36.00 over a trailing 30-day period or (y) a change in control transaction in which the price per share to the holders of the Company’s common stock is at least $36.00, as determined by the Company’s board of directors.

For the PSU awards, the Company used the Monte-Carlo option pricing model to determine the fair value of awards at the date of grant. The Monte-Carlo option pricing model uses similar input assumptions as the Black-Scholes model; however, it further incorporates into the fair-value determination the possibility that the market condition may not be satisfied. Compensation costs related to awards with a market-based condition are recognized regardless of whether the market condition is ultimately satisfied. Compensation cost is not reversed if the achievement of the market condition does not occur. The total grant date fair value of the PSU awards was determined to be $0.7 million and will be recognized as compensation expense over the weighted-average derived service period of approximately 4.3 years. The incremental fair value of the PSUs on the modification date of $31,000 are added to the unamortized value of the original grant of $569,000 and will be amortized to expense over the new implied service periods of 1.63 years to 2.79 years.

Performance and Market Contingent Stock Options

In January 2021, the board of directors modified 17,479 performance and market contingent stock options with vesting conditions that required the combination of a liquidity event, change of control or IPO with a market condition at prescribed levels. The modification removed the performance condition and lowered the market

conditions to a volume-weighted average per share closing trading price of the Company’s common stock of at least $18.00 over a trailing 30-day period for one tranche and at least $36.00 over a trailing 30-day period for the second tranche. The fair value of the options on the modification date of $81,000 will be amortized to expense over the implied service periods of 1.46 years to 2.52 years.

In June 2021, the board of directors modified 33,370 performance and market contingent stock options with vesting conditions that required the combination of a liquidity event, change of control or IPO with a market condition at prescribed levels. The modification removed the performance condition and adjusted the market conditions to a date on which the Company attains a valuation of at least one billion dollars measured by the volume-weighted average per share closing trading price of the Company’s common stock over a trailing 30-day period. The fair value of the options on the modification date of $102,000 will be amortized to expense over the implied service periods of 1.85 years.

Stock Based Compensation Expense

The following table sets forth the total stock-based compensation expense for all options granted to employees and nonemployees, including shares sold through the issuance of non-recourse promissory notes which are considered to be options for accounting purposes, and costs associated with the Company’s 2018 Employee Stock Purchase Plan (“2018 ESPP”) included in the Company’s condensed statements of operations and comprehensive loss (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Research and development	$	1,108	$	1,937	$	2,189	$	3,472
General and administrative		1,674		2,167		3,337		3,949
Total	$	2,782	$	4,104	$	5,526	$	7,421

There was no stock-based compensation expense related to awards accounted for as liability awards for the three and six months ended June 30, 2021, and the three months ended June 30, 2020. The Company recorded $0.1 million of expense related to awards accounted for as liability awards during the six months ended June 30, 2020.

Net Loss per Common Share - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Per Share (Details) - shares	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	11,729,522	10,457,637
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	8,625,251	9,468,522
Early Exercised Common Stock Subject to Future Vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	33,370	80,285
RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	2,990,123	840,642
Shares Subject to 2018 ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	80,778	68,188

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2021

Fair Value Disclosures [Abstract]

Summary of Financial Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis and Level of Inputs Used in Measurements

The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements were as follows (in thousands):

	June 30, 2021
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	9,498	$	9,498	$	—	$	—
Total cash equivalents		9,498		9,498		—		—
Short-term marketable securities:
U.S. government debt securities		9,037		—		9,037		—
U.S. treasuries		61,408		—		61,408		—
Total short-term marketable securities		70,445		—		70,445		—
Long-term marketable securities:
U.S. treasuries		11,497		—		11,497		—
U.S. government debt securities		2,045		—		2,045		—
Total long-term marketable securities		13,542		—		13,542		—
Total assets subject to fair value measurements on a recurring basis	$	93,485	$	9,498	$	83,987	$	—

	December 31, 2020
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents:
Money market funds	$	13,686	$	13,686	$	—	$	—
Total cash equivalents		13,686		13,686		—		—
Short-term marketable securities:
U.S. treasuries		55,349		—		55,349		—
U.S. and foreign commercial paper		11,999		—		11,999		—
U.S. and foreign corporate debt securities		1,001		—		1,001		—
U.S. government debt securities		11,543		—		11,543		—
Total short-term marketable securities		79,892		—		79,892		—
Long-term marketable securities:
U.S. treasuries		7,370		—		7,370		—
U.S. government debt securities		10,501		—		10,501		—
Total long-term marketable securities		17,871		—		17,871		—
Total assets subject to fair value measurements on a recurring basis	$	111,449	$	13,686	$	97,763	$	—

Summary of Reconciliation of Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs

	Amount
Balance at December 31, 2019	$	1,131
Additions		—
Settlements		—
Change in fair value		685
Balance at June 30, 2020	$	1,816

Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,782	$ 4,104	$ 5,526	$ 7,421
Research And Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,108	1,937	2,189	3,472
General And Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,674	$ 2,167	$ 3,337	$ 3,949

Corporate Restructuring

6 Months Ended

Jun. 30, 2021

Restructuring And Related Activities [Abstract]

Corporate Restructuring

10. Corporate Restructuring

In September 2020, the Company’s board of directors implemented a corporate restructuring to align its resources on cellular senescence programs in ophthalmology and neurology while further extending operating capital. The restructuring resulted in an elimination of approximately 33 positions, or approximately 32% of the Company’s workforce, as of September 30, 2020. The Company incurred a one-time employee benefits and severance charge of approximately $1.8 million in operating expenses during the year ended December 31, 2020. The related accrual is recorded in accrued compensation on the condensed balance sheet at December 31, 2020. Restructuring charges incurred under this plan primarily consisted of employee termination benefits. Employee termination benefits include severance costs, employee-related benefits, and supplemental one-time termination payments. Charges and other costs related to the workforce reduction and structure realignment, and non-cash share-based compensation credits related to the forfeiture of stock options are included in operating expenses in the condensed statements of operations and comprehensive loss. Of the total charge, $1.5 million was recorded to research and development expenses and $0.3 million was recorded to general and administrative expenses during the year ended December 31, 2020. Substantially all cash payments were paid out in the first quarter of 2021. The Company may also incur additional costs not currently contemplated due to events that may occur as a result of, or that are associated with, the restructuring.

Defined Contribution Plan - Additional Information (Details) - Defined Contribution Plan - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2019	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Contribution Plan Disclosure [Line Items]
Percent of employer matching contribution of employees' salary	4.00%
Defined Contribution Plan, Sponsor Location [Extensible List]	country:US
Matching Contributions		$ 0.1	$ 0.1	$ 0.3	$ 0.3

Commitments and Contingencies - Summary of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
2021 (remaining 6 months)	$ 3,343
2022	6,283
2023	4,810
2024	4,964
2025	5,123
Thereafter	22,179
Total future minimum lease payments	46,702
Less: Amount representing interest	(9,930)
Present value of future minimum lease payments	36,772
Less: Current portion of operating lease liability	(4,736)
Noncurrent portion of operating lease liability	$ 32,036	$ 34,468

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jan. 31, 2021	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation cost recognized			$ 200,000
Stock based compensation expense for liability awards				$ 0	$ 0	$ 0	$ 100,000
Performance and Market Contingent Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Trailing period	30 days
Modification date fair value	$ 102,000	$ 81,000
Implied service period for recognition	1 year 10 months 6 days
Performance and Market Contingent Stock Options \| Executive Team
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option awards exercisable upon the achievement of performance goals	33,370	17,479		33,370		33,370
Performance and Market Contingent Stock Options \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Implied service period for recognition		1 year 5 months 15 days
Attaining valuation of certain amount	$ 1,000,000,000
Performance and Market Contingent Stock Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Implied service period for recognition		2 years 6 months 7 days
Performance and Market Contingent Stock Options \| Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volume-weighted average per Share closing trading price		$ 18.00
Trailing period		30 days
Performance and Market Contingent Stock Options \| Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volume-weighted average per Share closing trading price		$ 36.00
Trailing period		30 days
2020 Employment Inducement Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance			1,100,000
Incremental fair value on modification date		$ 31,000				$ 31,000
Unamortized value of original grant		$ 569,000				$ 569,000
2020 Employment Inducement Incentive Plan \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance			800,000
2020 Employment Inducement Incentive Plan \| RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance			120,000
2020 Employment Inducement Incentive Plan \| PSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance			150,000
Grant date fair value			$ 700,000
Weighted-average derived service period for recognition			4 years 3 months 18 days
2020 Employment Inducement Incentive Plan \| PSUs \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
New implied service period for recognition		1 year 7 months 17 days
2020 Employment Inducement Incentive Plan \| PSUs \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
New implied service period for recognition		2 years 9 months 14 days
2020 Employment Inducement Incentive Plan \| PSUs \| Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance		50,000	50,000
Volume-weighted average per Share closing trading price		$ 18	$ 36.875
Trailing period		30 days	30 days
2020 Employment Inducement Incentive Plan \| PSUs \| Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance		100,000	100,000
Trailing period		30 days	30 days
Price per share to holders of company's common stock		$ 36.00	$ 36.875
Market capitalization trigger			$ 2,500,000,000
2020 Employment Inducement Incentive Plan \| RSUs and Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights			The stock options and RSUs will vest subject to continued service through the applicable vesting date.
2020 Employment Inducement Incentive Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance			30,000
Number of shares vested			30,000

Commitments and Contingencies -Summary of Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lease, Cost [Abstract]
Operating lease cost	$ 1,091	$ 1,144	$ 2,187	$ 2,444
Variable lease cost	387	363	853	641
Sublease income	(390)		(535)
Impairment of operating lease right-of-use asset				1,157
Total lease cost	$ 1,088	$ 1,507	$ 2,505	$ 4,242

Summary of Significant Accounting Policies - Additional Information (Details)	6 Months Ended
	Jun. 30, 2021 USD ($)
Accounting Policies [Abstract]
Off-balance sheet concentrations of credit risk description	As of June 30, 2021, the Company had no off-balance sheet concentrations of credit risk.
Off-balance sheet concentrations of credit risk	$ 0

Fair Value Measurements - Summary of Reconciliation of Financial Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) - Fair Value, Recurring - Level 3 $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance at December 31, 2019	$ 1,131
Change in fair value	685
Balance at June 30, 2020	$ 1,816

Net Loss per Common Share (Tables)

6 Months Ended

Jun. 30, 2021

Earnings Per Share [Abstract]

Schedule of Reconciliation of Numerators and Denominators Used In Computing Net Loss From Continuing Operations Per Share

A reconciliation of the numerators and denominators used in computing net loss from continuing operations per share is as follows (in thousands, except share and per share amounts):

	Three Months Ended June 30,						Six Months Ended June 30,
	2021			2020			2021			2020
Numerator:
Net loss	$	(17,826	)	$	(18,667	)	$	(33,582	)	$	(46,705	)
Denominator:
Weighted-average number of shares outstanding—basic and diluted		54,859,727			49,659,153			54,516,445			48,606,768
Net loss per share—basic and diluted	$	(0.32	)	$	(0.38	)	$	(0.62	)	$	(0.96	)

Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Per Share

Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows:

	June 30,
	2021		2020
Options to purchase common stock		8,625,251		9,468,522
Early exercised common stock subject to future vesting		33,370		80,285
RSUs		2,990,123		840,642
Shares subject to 2018 ESPP		80,778		68,188
Total		11,729,522		10,457,637

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

	Number of Shares			Weighted- Average Exercise Price
Balances at December 31, 2020		7,475,472		$	6.88
Granted		2,638,838		$	5.23
Exercised		(430,047	)	$	3.64
Canceled		(1,059,012	)	$	9.09
Balances at June 30, 2021		8,625,251		$	6.27

Summary of Restricted Stock Units, Performance Stock Units and Restricted Stock Awards Activity

	Number of Shares			Weighted- Average Grant Date Fair Value
Unvested at December 31, 2020		2,922,077		$	3.44
Granted		536,723		$	5.02
Vested		(111,297	)	$	6.58
Canceled		(357,380	)	$	3.35
Unvested at June 30, 2021		2,990,123		$	3.62

Summary of Stock-based Compensation Expense

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Research and development	$	1,108	$	1,937	$	2,189	$	3,472
General and administrative		1,674		2,167		3,337		3,949
Total	$	2,782	$	4,104	$	5,526	$	7,421

Corporate Restructuring - Additional Information (Details) $ in Millions	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2021	Sep. 30, 2020 Position	Dec. 31, 2020 USD ($)
Restructuring Cost And Reserve [Line Items]
Restructuring implementation date	Sep. 30, 2020
Number of positions eliminated \| Position		33
Percentage of positions eliminated		32.00%
Severance charge in operating expenses			$ 1.8
Research And Development Expense
Restructuring Cost And Reserve [Line Items]
Severance charge in operating expenses			1.5
General And Administrative Expense
Restructuring Cost And Reserve [Line Items]
Severance charge in operating expenses			$ 0.3

Marketable Securities

6 Months Ended

Jun. 30, 2021

Investments Debt And Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

Marketable securities, which are classified as available-for-sale, consisted of the following as of June 30, 2021 (in thousands):

	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	$	9,498	$	—	$	—		$	9,498
Total cash equivalents		9,498		—		—			9,498
Short-term marketable securities:
U.S. government debt securities		9,035		2		—			9,037
U.S. treasuries		61,401		8		(1	)		61,408
Total short-term marketable securities		70,436		10		(1	)		70,445
Long-term marketable securities:
U.S. treasuries		11,502		—		(5	)		11,497
U.S. government debt securities		2,044		1		—			2,045
Total long-term marketable securities		13,546		1		(5	)		13,542
Total	$	93,480	$	11	$	(6	)	$	93,485

Marketable securities, which are classified as available-for-sale, consisted of the following as of December 31, 2020 (in thousands):

	Amortized Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	$	13,686	$	—	$	—		$	13,686
Total cash equivalents		13,686		—		—			13,686
Short-term marketable securities:
U.S. and foreign commercial paper		11,998		1		—			11,999
U.S. and foreign corporate debt securities		1,001		—		—			1,001
U.S. government debt securities		11,541		2		—			11,543
U.S. treasuries		55,350		2		(3	)		55,349
Total short-term marketable securities		79,890		5		(3	)		79,892
Long-term marketable securities
U.S. treasuries		7,369		1		—			7,370
U.S. government debt securities		10,498		3		—			10,501
Total long-term marketable securities		17,867		4		—			17,871
Total	$	111,443	$	9	$	(3	)	$	111,449

At June 30, 2021, the remaining contractual maturities of available-for-sale securities were less than two years. There have been no significant realized gains or losses on available-for-sale securities for the periods presented. Available-for-sale debt securities that were in a continuous loss position but were not deemed to be other than temporarily impaired were immaterial at both June 30, 2021 and December 31, 2020. The Company does not intend to and believes it is not more likely than not that it will be required to sell these debt securities before their maturities.

See Note 3, “Fair Value Measurements,” for further information regarding the fair value of the Company’s financial instruments.

Commitments and Contingencies - Additional Information (Details)	1 Months Ended			3 Months Ended	6 Months Ended
	Jun. 30, 2021 USD ($) ft² $ / ft²	May 31, 2021 ft² $ / ft²	Feb. 28, 2021 USD ($) ft² $ / ft²	Jun. 30, 2021 USD ($) ft²	Jun. 30, 2021 USD ($) ft²	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Commitments And Contingencies [Line Items]
Sublease income				$ 390,000	$ 535,000
South San Francisco, California
Commitments And Contingencies [Line Items]
Lessee, operating lease, description					In February 2019, the Company entered into a lease agreement for new office and laboratory space in South San Francisco, California. The term of the lease agreement commenced in May 2019. The lease has an initial term from occupancy of approximately ten years ending on December 31, 2029 with an option to extend the term for an additional eight years at then-market rental rates
Lease commencement date					2019-05
Lease expiration date					Dec. 31, 2029
Operating lease, initial lease term	10 years			10 years	10 years
Operating lease, option to extend description					option to extend the term for an additional eight years
Operating lease, existence of option to extend					true
Operating lease, renewal term	8 years			8 years	8 years
Tenant improvement allowance							$ 10,700,000
Letter of credit, delivered in connection of lease agreement	$ 900,000			$ 900,000	$ 900,000
Estimated discount rate	3.50%			3.50%	3.50%
Impairment loss						$ 2,200,000
Space subleased (in sqaure feet) \| ft²	23,000			23,000	23,000
Sublease expiration date	Aug. 31, 2024
Sublease rent per square foot \| $ / ft²	6.25
Annual percentage increase in sublease base rent	3.50%
Percentage of operating expenses and property management fees to be paid by subtenant	37.00%			37.00%	37.00%
Brisbane, California
Commitments And Contingencies [Line Items]
Operating lease, option to extend description					The lease agreement includes an escalation clause for increased rent and a renewal provision allowing the Company to extend this lease for an additional four years by giving the landlord written notice of the election to exercise the option at least fifteen months prior to the original expiration of the lease term.
Operating lease, renewal term	4 years			4 years	4 years
Tenant improvement allowance	$ 3,900,000			$ 3,900,000	$ 3,900,000
Lease expiration date					2022-10
Impairment loss				0	$ 0
Space subleased (in sqaure feet) \| ft²		11,500	27,000
Sublease expiration date		Sep. 30, 2022	Aug. 31, 2022
Sublease rent per square foot \| $ / ft²		1.00	3.53
Annual percentage increase in sublease base rent			3.00%
Percentage of operating expenses and property management fees to be paid by subtenant		30.00%	41.00%
Incurred initial direct costs of sublease			$ 100,000
Sublease income				$ 400,000	$ 500,000

Fair Value Measurements - Summary of Financial Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis and Level of Inputs Used in Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets:
Short-term marketable securities	$ 70,445	$ 79,892
Long-term marketable securities	13,542	17,871
Fair Value, Recurring
Assets:
Cash equivalents	9,498	13,686
Short-term marketable securities	70,445	79,892
Long-term marketable securities	13,542	17,871
Total assets subject to fair value measurements on a recurring basis	93,485	111,449
Fair Value, Recurring \| Level 1
Assets:
Cash equivalents	9,498	13,686
Total assets subject to fair value measurements on a recurring basis	9,498	13,686
Fair Value, Recurring \| Level 2
Assets:
Short-term marketable securities	70,445	79,892
Long-term marketable securities	13,542	17,871
Total assets subject to fair value measurements on a recurring basis	83,987	97,763
Money market funds \| Fair Value, Recurring
Assets:
Cash equivalents	9,498	13,686
Money market funds \| Fair Value, Recurring \| Level 1
Assets:
Cash equivalents	9,498	13,686
U.S. government debt securities \| Fair Value, Recurring
Assets:
Short-term marketable securities	9,037	11,543
Long-term marketable securities	2,045	10,501
U.S. government debt securities \| Fair Value, Recurring \| Level 2
Assets:
Short-term marketable securities	9,037	11,543
Long-term marketable securities	2,045	10,501
U.S. Treasuries \| Fair Value, Recurring
Assets:
Short-term marketable securities	61,408	55,349
Long-term marketable securities	11,497	7,370
U.S. Treasuries \| Fair Value, Recurring \| Level 2
Assets:
Short-term marketable securities	61,408	55,349
Long-term marketable securities	$ 11,497	7,370
U.S. and foreign commercial paper \| Fair Value, Recurring
Assets:
Short-term marketable securities		11,999
U.S. and foreign commercial paper \| Fair Value, Recurring \| Level 2
Assets:
Short-term marketable securities		11,999
U.S. and foreign corporate debt securities \| Fair Value, Recurring
Assets:
Short-term marketable securities		1,001
U.S. and foreign corporate debt securities \| Fair Value, Recurring \| Level 2
Assets:
Short-term marketable securities		$ 1,001

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

These condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and the rules and regulations of the United States Securities and Exchange Commission (“SEC”) for interim reporting.

Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted. Accordingly, the unaudited condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 filed with the SEC.

Unaudited Condensed Financial Statements

The accompanying financial information for the three and six months ended June 30, 2021 and 2020 are unaudited. The unaudited condensed financial statements have been prepared on the same basis as the annual audited financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring

adjustments, necessary to present fairly the Company’s financial position as of June 30, 2021 and its results of operations for the three and six months ended June 30, 2021 and 2020 and cash flows for the six months ended June 30, 2021 and 2020. The results for interim periods are not necessarily indicative of the results expected for the full fiscal year or any other periods.

Use of Estimates

The condensed financial statements have been prepared in accordance with GAAP, which requires management to make estimates and assumptions that affect the amounts and disclosures reported in the condensed financial statements and accompanying notes. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s condensed balance sheets and the amount of expenses and income reported for each of the periods presented are affected by estimates and assumptions, which are used for, but are not limited to, determining the fair value of assets and liabilities, contingent consideration liability, the fair value of right-of-use assets and lease liabilities, and stock-based compensation. Actual results could differ from such estimates or assumptions.

Segments

The Company has one operating segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of allocating resources.

Cash, Cash Equivalents, and Restricted Cash

The Company considers all highly liquid investments with original maturities of 90 days or less from the date of purchase to be cash equivalents. Cash equivalents primarily include money market funds that invest in U.S. Treasury obligations which are stated at fair value.

The Company has issued letters of credit under lease agreements which have been collateralized. This cash is classified as noncurrent restricted cash on the balance sheet based on the term of the underlying lease.

	June 30, 2021		December 31, 2020
Cash and cash equivalents	$	13,498	$	17,807
Restricted cash		1,446		1,446
Total cash, cash equivalents, and restricted cash	$	14,944	$	19,253

Marketable Securities

The Company generally invests its excess cash in investment grade, short to intermediate-term, fixed income securities. Such investments are considered available-for-sale debt securities and reported at fair value with unrealized gains and losses included as a component of stockholders’ equity. Marketable securities with original maturities of greater than 90 days from the date of purchase but less than one year from the balance sheet date that are available to be converted into cash to fund current operations are classified as short-term, while marketable securities with maturities in one year or beyond one year from the balance sheet date are classified as long-term. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in interest income on the statements of operations and comprehensive loss. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on marketable securities are included in other expense. The cost of securities sold is determined using the specific identification method.

The Company periodically evaluates whether declines in fair values of its marketable securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the marketable security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any marketable securities before recovery of its amortized cost basis. Factors considered include quoted market prices, recent financial results and operating trends, implied values from any recent transactions or offers of investee securities, credit quality of debt instrument issuers,

other publicly available information that may affect the value of the marketable security, duration and severity of the decline in value, and management’s strategy and intentions for holding the marketable security. To date, the Company has not recorded any impairment charges on its marketable securities related to other-than-temporary declines in market value.

Fair Value Measurements

The Company’s financial instruments during the periods presented consist of cash and cash equivalents, restricted cash, marketable securities, prepaid expenses and other current assets, accounts payable, accrued compensation, accrued and other current liabilities, and long-term debt. Fair value estimates of these instruments are made at a specific point in time, based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of judgment.

Concentrations of Risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, restricted cash, and marketable securities. Substantially all of the Company’s cash and cash equivalents and restricted cash is deposited in accounts with financial institutions that management believes are of high credit quality. Such deposits have and will continue to exceed federally insured limits. The Company maintains its cash with accredited financial institutions and accordingly, such funds are subject to minimal credit risk. The Company has not experienced any losses on its cash deposits.

The Company’s investment policy limits investments in marketable securities to certain types of securities issued by the U.S. government, its agencies and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The Company is exposed to credit risk in the event of a default by the financial institutions holding its cash, cash equivalents, restricted cash, and marketable securities and issuers of marketable securities to the extent recorded on the balance sheets. As of June 30, 2021, the Company had no off-balance sheet concentrations of credit risk.

The Company depends on third-party suppliers for key raw materials used in its manufacturing processes and is subject to certain risks related to the loss of these third-party suppliers or their inability to supply the Company with adequate raw materials.

In March 2020, the World Health Organization declared the COVID-19 outbreak a pandemic. To date, the Company’s operations have not been significantly impacted by the COVID-19 pandemic. However, the Company cannot at this time predict the specific extent, duration, or full impact that the COVID-19 pandemic will have on its financial condition and results of operations, including ongoing and planned clinical studies. The impact of the COVID-19 pandemic on the financial performance of the Company will depend on future developments. These developments and the impact of the COVID-19 pandemic on the financial markets and the overall economy are highly uncertain. The Company continues to monitor the impact the COVID-19 pandemic may have on the clinical development of its product candidates, including potential delays or modifications to its ongoing and planned studies.

Research and Development Expenses and Accruals

Costs related to research, design, and development of drug candidates are charged to research and development expense as incurred. Research and development costs include, but are not limited to, payroll and personnel expenses for personnel contributing to research and development activities, laboratory supplies, outside services, licenses acquired to be used in research and development, manufacturing of clinical material, pre-clinical testing and consultants and allocated overhead, including rent, equipment, depreciation, and utilities. Research and development costs are expensed as incurred unless there is an alternative future use in other research and development projects. Payments made prior to the receipt of goods or services to be used in research and development are deferred and recognized as expense in the period in which the related goods are received or services are rendered. Such payments are evaluated for current or long-term classification based on when they will be realized.

As part of the process of preparing its condensed financial statements, the Company is required to estimate expenses resulting from its obligations under contracts with vendors and consultants and clinical site agreements in connection with conducting clinical trials. The financial terms of these contracts are subject to negotiations which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided under such contracts. The Company’s objective is to reflect the appropriate expenses in its condensed financial statements by matching those expenses with the period in which services and efforts are

expended. The Company accounts for these expenses according to the progress of the production of clinical trial materials or based on progression of the clinical trial, as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates by taking into account discussion with applicable personnel and outside service providers as to the progress or state of consummation of goods and services, or the services completed.

During the course of a clinical trial, the rate of expense recognition is adjusted if actual results differ from the Company’s estimates. The Company makes estimates of accrued expenses as of each balance sheet date in its condensed financial statements based on the facts and circumstances known at that time. The clinical trial accrual is dependent in part upon the timely and accurate reporting of contract research organizations, contract manufacturers, and other third-party vendors. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in reporting changes in estimates in any particular period. Adjustments to prior period estimates have not been material for the six months ended June 30, 2021 and 2020.

Contingent Consideration Liability

The Company has entered into and may continue to enter into, license agreements to access and utilize certain technology. In each case, the Company evaluates whether the license agreement results in the acquisition of an asset or a business. To date, all of the Company’s license agreements have been considered acquisitions of assets and none have been considered acquisitions of a business. For license agreements that are considered to be acquisitions of assets, the upfront payments for such license, as well as any future milestone payments made before product approval, are immediately recognized as research and development expense when due, provided there is no alternative future use of the rights in other research and development projects. Some of the Company’s license agreements also include contingent consideration in the form of an obligation to issue additional shares of the Company’s common stock based on the achievement of certain milestones. The Company assesses on a continuous basis whether (i) such contingent consideration meets the definition of a derivative, and (ii) whether it can be classified within stockholders’ equity. Until such time when equity classification criteria are met or the milestones expire, the contingent consideration is classified as a liability. The derivative related to this contingent consideration is measured at fair value as of each balance sheet date with the related change in fair value being reflected in operating expenses. Upon a reassessment event that results in the contingent consideration no longer meeting the definition of a derivative and/or meeting equity classification criteria, the final change in fair value of the instrument is recorded within operating expenses and the liability is reclassified into stockholders’ equity.

Property and Equipment, Net

Property and equipment are stated at cost, less accumulated depreciation. Depreciation is calculated using the straight-line method over the estimated useful lives of the respective assets, generally three years. Leasehold improvements are amortized on a straight-line basis over the shorter of their estimated useful lives or the term of the lease. Depreciation and amortization begin at the time the asset is placed in service. Maintenance and repairs are charged to expense as incurred and costs of improvement are capitalized.

Leases

The Company determines whether the arrangement is or contains a lease at the inception of the arrangement and if so, whether such a lease is classified as a financing lease or an operating lease. Operating leases are included in operating lease right-of-use assets, (“ROU assets”), operating lease liabilities, net of current portion, and accrued and other current liabilities on the Company’s condensed balance sheets. The Company has elected not to recognize on the condensed balance sheets leases with terms of one year or less. Operating lease ROU assets represent the Company’s right to use an underlying asset for the lease term and are considered long-lived assets for purposes of identifying, recognizing and measuring impairment. Operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of lease payments over the expected lease term. As the Company’s leases do not provide an implicit rate, the Company uses its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment, in determining the present value of lease payments. The operating lease ROU asset also includes any lease payments made or incentives received and impairment charges if the Company determines the ROU asset is impaired and excludes lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise such options to extend or terminate the lease. Lease expense for lease payments is recognized on a straight-line basis over the lease term.

The Company has elected to not separate lease and non-lease components for its leased assets and accounts for all lease and non-lease components of its agreements as a single lease component. The lease components resulting in a ROU asset have been recorded on the condensed balance sheets and are amortized as lease expense on a straight-line basis over the lease term.

The Company has subleased all of its Brisbane, California facility and a portion of its South San Francisco, California facility under agreements considered to be operating leases according to ASC 842. The Company has not been legally released from its primary obligations under the original leases and therefore it continues to account for the original leases as it did before commencement of the subleases. The Company records both fixed and variable payments received from the sublessee in its statements of operations on a straight-line basis as an offset to rent expense.

The Company does not have any material financing leases.

Income Taxes

On March 18, 2020, the Families First Coronavirus Response Act (“FFCR Act”), and on March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) were each enacted in response to the COVID-19 pandemic. The FFCR Act and the CARES Act contain numerous tax-related provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property.

On June 29, 2020 California State Assembly Bill 85 (the “Trailer Bill”) was enacted which suspends the use of California net operating loss (“NOL”) deductions and certain tax credits, including research and development tax credits, for the 2020, 2021, and 2022 tax years.

In December 2020, the Consolidated Appropriations Act, 2021 (the “CAA”) was signed into law. The CAA included additional funding through tax credits as part of its economic package for 2021.

The FFCR Act, CARES Act, Trailer Bill, and CAA did not have a material impact on the Company’s condensed financial statements as of June 30, 2021; however, the Company continues to examine the impacts the FFCR Act, CARES Act, and Trailer Bill may have on its business, results of operations, financial condition, and liquidity.

Net Loss per Common Share

Basic net loss per share is calculated by dividing net loss by the weighted average number of shares outstanding for the period. Diluted net loss per share is calculated by dividing net loss by the weighted average number of shares of common stock and potential dilutive common stock equivalents outstanding during the period if the effect is dilutive. Since the Company was in a loss position for all periods presented, basic net loss per share is the same as diluted net loss per share as the effects of potentially dilutive securities are antidilutive. The calculation of diluted earnings (loss) per share also requires that, to the extent the presumed issuance of additional shares as contingent consideration is dilutive to earnings (loss) per share for the period, adjustments to net income or net loss used in the calculation are required to remove the change in fair value of the contingent consideration liability for the period. Likewise, adjustments to the denominator are required to reflect the related dilutive shares. In all periods presented, the Company’s outstanding stock options, convertible preferred stock, early exercised common stock subject to future vesting, restricted stock accounted for as options common and preferred stock warrants and presumed issuance of additional shares as contingent consideration were excluded from the calculation of diluted net loss per share because their effects were antidilutive.

Comprehensive Loss

Comprehensive loss includes net loss and certain changes in stockholders’ equity (deficit) that are excluded from net loss, primarily unrealized losses on the Company’s marketable securities.

Recently Issued Accounting Pronouncements Not Yet Adopted

In October 2020, the FASB issued ASU 2020-10, Codification Improvements. The ASU contains improvements to the Codification by ensuring that all guidance that requires or provides an option for an entity to provide information in the notes to financial statements is codified in the disclosure section of the Codification. The ASU also improves

various topics in the Codification so that entities can apply guidance more consistently on codifications that are varied in nature where the original guidance may have been unclear. The amendments in ASU 2020-10 are effective for the Company for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. Early adoption is permitted. The Company does not expect the adoption of ASU 2020-10 to have a material impact on its condensed financial statements and related disclosures.

In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity. ASU 2020-06 eliminates the beneficial conversion and cash conversion accounting models for convertible instruments. It also amends the accounting for certain contracts in an entity’s own equity that are currently accounted for as derivatives because of specific settlement provisions. In addition, ASU 2020-06 modifies how particular convertible instruments and certain contracts that may be settled in cash or shares impact the diluted EPS computation. The amendments in ASU 2020-06 are effective for smaller reporting companies as defined by the SEC for fiscal years beginning after December 15, 2023, including interim periods within those fiscal years. Early adoption is permitted, but no earlier than fiscal years beginning after December 15, 2020. The Company is currently evaluating the impact of ASU 2020-06 on its condensed financial statements.

In August 2018, the FASB issued ASU No. 2018-15, Intangibles (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This new standard also requires customers to expense the capitalized implementation costs of a hosting arrangement that is a service contract over the term of the hosting arrangement. This standard is effective for the Company for annual reporting periods beginning after December 15, 2020, and interim periods within annual periods beginning after December 15, 2021. This new standard can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company is currently evaluating the impact of adoption on its condensed financial statements.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments, as clarified in subsequent amendments. ASU 2016-13 changes the impairment model for certain financial instruments. The new model is a forward-looking expected loss model and will apply to financial assets subject to credit losses and measured at amortized cost and certain off-balance sheet credit exposures. This includes loans, held-to-maturity debt securities, loan commitments, financial guarantees and net investments in leases, as well as trade receivables. For available-for-sale debt securities with unrealized losses, credit losses will be measured in a manner similar to today, except that the losses will be recognized as allowances rather than reductions in the amortized cost of the securities. In October 2019, the FASB voted to delay the effective date of this standard. Topic 326 will be effective for the Company for fiscal years beginning after December 15, 2022. Early adoption is permitted. The Company is currently assessing the effect that this ASU will have on its condensed financial position, results of operations, and disclosures.

Net Loss per Common Share - Schedule of Reconciliation of Numerators and Denominators Used In Computing Net Loss From Continuing Operations Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net loss	$ (17,826)	$ (15,756)	$ (18,667)	$ (28,038)	$ (33,582)	$ (46,705)
Denominator:
Weighted-average number of shares outstanding—basic and diluted	54,859,727		49,659,153		54,516,445	48,606,768
Net loss per share, basic and diluted	$ (0.32)		$ (0.38)		$ (0.62)	$ (0.96)

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669619-108580

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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+ Details

Related Party Transactions

6 Months Ended

Jun. 30, 2021

Related-Party Transactions

8. Related Party Transactions

In January 2018, the Company issued full-recourse promissory notes to a non-executive officer employee of the Company for an aggregate principal amount of $0.2 million with an interest rate of 2.5% per annum. All of the principal was used to early exercise options for 59,322 shares of the Company’s common stock. In December 2019, the full recourse note was deemed satisfied and superseded by a new full recourse promissory note agreement with a principal amount of $0.2 million and an interest rate of 1.51% per annum. In January 2021, the non-executive officer employee terminated his employment with the Company. As at March 31, 2021 the Company reclassified the $0.2 million recorded on the balance sheet in stockholders’ equity as ‘Related party promissory note for purchase of common stock’ to ‘Promissory notes for purchase of common stock’. The balance was repaid in full during the three months ended June 30, 2021.

Stock-Based Compensation - Summary of Stock Option Activity (Details)	6 Months Ended
	Jun. 30, 2021 $ / shares shares
Number of Shares
Balances at December 31, 2020 \| shares	7,475,472
Granted \| shares	2,638,838
Exercised \| shares	(430,047)
Canceled \| shares	(1,059,012)
Balances at June 30, 2021 \| shares	8,625,251
Weighted-Average Exercise Price
Balances at December 31, 2020 \| $ / shares	$ 6.88
Granted \| $ / shares	5.23
Exercised \| $ / shares	3.64
Canceled \| $ / shares	9.09
Balances at June 30, 2021 \| $ / shares	$ 6.27

Defined Contribution Plan

6 Months Ended

Jun. 30, 2021

Compensation And Retirement Disclosure [Abstract]

Defined Contribution Plan

13. Defined Contribution Plan

The Company sponsors a 401(k) Plan that stipulates that eligible employees can elect to contribute to the 401(k) Plan, subject to certain limitations, on a pretax basis. In January 2019, the Company began to match 4% of employees’ salary. During the three and six months ended June 30, 2021, the Company recorded matching contributions of $0.1 million and $0.3 million, respectively. During the three and six months ended June 30, 2020, the Company recorded matching contributions of $0.1 million and $0.3 million, respectively.

- Definition

The entire disclosure for retirement benefits.

+ References

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+ Details

License Agreements and Strategic Investment - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Research And Development Arrangement Contract To Perform For Others [Line Items]
Common stock, shares issued	55,104,250			55,104,250		53,253,213
Compound library and option agreement execution month and year				2016-02
Licensed Products
Research And Development Arrangement Contract To Perform For Others [Line Items]
Royalties due from sales				$ 0
Commercial Agreements \| Clinical Stage Biopharmaceutical Company
Research And Development Arrangement Contract To Perform For Others [Line Items]
Common stock, shares issued	974,980			974,980
Milestone payments	$ 2,000,000.0
Equity payments percentage				80.00%
Contingent consideration liability	0			$ 0
Strategic investments	0			$ 0		$ 0
Change in fair value of investment			$ 4,400,000		$ 3,100,000
Funding provided for the research and development under the agreement in period				2020-02
Commercial Agreements \| Clinical Stage Biopharmaceutical Company \| Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Contingent consideration additional common stock issued for one licensed product				933,337
Contingent consideration additional common stock issued for two or more licensed product				1,333,338
Milestone payments				$ 70,300,000
Funding provided for the research and development under the agreement	$ 2,000,000.0			$ 2,000,000.0
Commercial Agreements \| Clinical Stage Biopharmaceutical Company \| Initial License Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
License agreement execution month and year				2016-02
Commercial Agreements \| Clinical Stage Biopharmaceutical Company \| Second License Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
License agreement execution month and year				2019-01
Commercial Agreements \| Academic Institution
Research And Development Arrangement Contract To Perform For Others [Line Items]
Common stock, shares issued	186,667			186,667
Equity payments percentage				20.00%
Other Licensing Agreements with Research Institutions
Research And Development Arrangement Contract To Perform For Others [Line Items]
Contingent consideration, milestone or royalty payments	$ 0			$ 0		$ 0
Other Licensing Agreements with Research Institutions \| UCSF
Research And Development Arrangement Contract To Perform For Others [Line Items]
Common shares expected to be issued		34,000
Contingent consideration, milestone or royalty payments	$ 0			$ 0
Maximum milestone payments for each product licensed under agreement		$ 13,600,000
Other Licensing Agreements with Research Institutions \| UCSF \| Common Stock
Research And Development Arrangement Contract To Perform For Others [Line Items]
Issuance of common stock		120,000
Other Licensing Agreements with Research Institutions \| UCSF \| Additional Paid-In Capital
Research And Development Arrangement Contract To Perform For Others [Line Items]
Common stock issued to third parties		$ 1,000,000.0

Term Loan Facility (Tables)

6 Months Ended

Jun. 30, 2021

Debt Disclosure [Abstract]

Schedule of Future Principal Payments for Long-Term Debt

Future principal payments for the long-term debt are as follows (in thousands):

	June 30, 2021
2021 (for the remaining 6 months)	$	—
2022		3,838
2023		12,272
2024		8,890
Total principal payments		25,000
End of term fee due at maturity in 2024		1,562
Total principal and end of term fee payments		26,562
Unamortized discount and debt issuance costs		(1,670	)
Long-term debt, net	$	24,892

Fair Value Measurements - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Transfers into and out of fair value hierarchy	$ 0	$ 0

Organization - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (372,881)				$ (372,881)		$ (339,299)
Net loss	(17,826)	$ (15,756)	$ (18,667)	$ (28,038)	(33,582)	$ (46,705)
Cash used in operations					(28,475)	$ (44,357)
Cash, cash equivalents and marketable securities	$ 97,500				$ 97,500

- Definition

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

+ References

+ Details

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2021

Accounting Policies [Abstract]

Basis of Presentation

Unaudited Condensed Financial Statements

Use of Estimates

Segments

Cash, Cash Equivalents and Restricted Cash

	June 30, 2021		December 31, 2020
Cash and cash equivalents	$	13,498	$	17,807
Restricted cash		1,446		1,446
Total cash, cash equivalents, and restricted cash	$	14,944	$	19,253

Marketable Securities

Fair Value Measurements

Concentrations of Risk

Research and Development Expenses and Accruals

Contingent Consideration Liability

Property and Equipment, Net

Leases

The Company does not have any material financing leases.

Income Taxes

In December 2020, the Consolidated Appropriations Act, 2021 (the “CAA”) was signed into law. The CAA included additional funding through tax credits as part of its economic package for 2021.

Net Loss per Common Share

Comprehensive Loss

Comprehensive loss includes net loss and certain changes in stockholders’ equity (deficit) that are excluded from net loss, primarily unrealized losses on the Company’s marketable securities.

Recently Issued Accounting Pronouncements Not Yet Adopted

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating expenses:
Research and development	$ 11,016	$ 16,123	$ 19,733	$ 35,388
General and administrative	5,980	6,320	12,206	12,273
Change in fair value of contingent consideration	0	906	0	685
Impairment of long-lived assets	0	0	0	2,159
Total operating expenses	16,996	23,349	31,939	50,505
Loss from operations	(16,996)	(23,349)	(31,939)	(50,505)
Interest income	26	340	62	867
Interest expense	(784)	0	(1,559)	0
Other income (expense), net	(72)	4,342	(146)	2,933
Net loss	(17,826)	(18,667)	(33,582)	(46,705)
Other comprehensive gain (loss)
Unrealized gain (loss) on marketable debt securities	(10)	(141)	0	142
Comprehensive loss	$ (17,836)	$ (18,808)	$ (33,582)	$ (46,563)
Net loss per share, basic and diluted	$ (0.32)	$ (0.38)	$ (0.62)	$ (0.96)
Weighted-average number of shares used in computing net loss per share, basic and diluted	54,859,727	49,659,153	54,516,445	48,606,768

Equity Financing - Additional Information (Details) - USD ($)		1 Months Ended		3 Months Ended				6 Months Ended		12 Months Ended
	Jul. 31, 2020	Jul. 31, 2020	Jun. 30, 2019	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Subsidiary Sale Of Stock [Line Items]
Equity financing, authorized amount			$ 250,000,000.0
Proceeds from sale of common stock								$ 8,893,000	$ 29,494,000
At-the-Market Equity Offering Program \| Cowen \| June 2019 Sales Agreement
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock (in shares)								1,187,068		5,002,257
Proceeds from sale of common stock										$ 37,300,000
Payments for other offering expenses										$ 1,300,000
At-the-Market Equity Offering Program \| Cowen \| June 2019 Sales Agreement \| Maximum
Subsidiary Sale Of Stock [Line Items]
Equity financing, authorized amount			$ 75,000,000.0
Percentage of gross sales proceeds of common stock payable as compensation			3.00%
At-the-Market Equity Offering Program \| Cowen \| July 2020 Sales Agreement
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock (in shares)				0				33,561
Proceeds from sale of common stock								$ 8,900,000
Payments for other offering expenses								$ 300,000
At-the-Market Equity Offering Program \| Cowen \| July 2020 Sales Agreement \| Maximum
Subsidiary Sale Of Stock [Line Items]
Equity financing, authorized amount	$ 50,000,000.0
Percentage of gross sales proceeds of common stock payable as compensation	3.00%
At-the-Market Equity Offering Program \| Common Stock
Subsidiary Sale Of Stock [Line Items]
Equity financing, authorized amount		$ 50,000,000.0	$ 75,000,000.0
Issuance of common stock (in shares)					1,220,629	2,594,030	1,513,840

Term Loan Facility - Additional Information (Details)		3 Months Ended		6 Months Ended
Term Loan Facility - Additional Information (Details)	Aug. 03, 2020 USD ($) Tranche	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jul. 01, 2021 USD ($)
Debt Instrument [Line Items]
Debt instrument aggregate principal amount		$ 25,000,000		$ 25,000,000
Total principal payments		25,000,000		25,000,000
Unamortized discount and debt issuance costs		1,670,000		1,670,000
End of term fee due at maturity		1,562,000		1,562,000
Interest expense		784,000	$ 0	1,559,000	$ 0
Term Loan \| Loan Agreement \| Hercules Capital
Debt Instrument [Line Items]
Debt instrument aggregate principal amount		$ 25,000,000.0		$ 25,000,000.0
Number of tranches \| Tranche	4
Principal amount of first tranche	$ 25,000,000.0
Long-term debt, maturity date		Aug. 01, 2024		Aug. 01, 2024
Final payment fee of the total term loan advanced				6.25%
Debt instrument, interest rate terms				Interest on the term loan accrues at a per annum rate equal to the greater of (i) the Wall Street Journal prime rate plus 6.10% and (ii) 9.35%. On June 30, 2021, the rate was 9.35 %. Interest expense is calculated using the effective interest method and is inclusive of non-cash amortization of capitalized loan issuance costs. At June 30, 2021, the effective interest rate was 12.40%.
Debt instrument, interest rate, stated percentage		9.35%		9.35%
Debt instrument, interest rate, effective percentage		12.40%		12.40%
Maximum amount of debt that can be purchased by lender.				$ 2,000,000.0
Total principal payments		$ 25,000,000.0		25,000,000.0
Unamortized discount and debt issuance costs		1,700,000		1,700,000
End of term fee due at maturity		1,600,000		1,600,000
Term Loan \| Loan Agreement \| Hercules Capital \| Interest And Other Expense
Debt Instrument [Line Items]
Interest expense		$ 800,000	$ 0	$ 1,600,000	$ 0
Term Loan \| Loan Agreement \| Hercules Capital \| Subsequent Event
Debt Instrument [Line Items]
Debt instrument, minimum unrestricted cash						$ 15,000,000.0
Term Loan \| Loan Agreement \| Hercules Capital \| Wall Street Journal Prime Rate
Debt Instrument [Line Items]
Debt instrument, interest rate, basis spread on variable rate				6.10%
Term Loan \| Loan Agreement \| Hercules Capital \| Maximum
Debt Instrument [Line Items]
Debt instrument aggregate principal amount	80,000,000.0
Prepayment fee				1.50%
Total principal payments	$ 80,000,000.0

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 13,498	$ 17,807
Short-term marketable securities	70,445	79,892
Prepaid expenses and other current assets	3,665	3,167
Total current assets	87,608	100,866
Property and equipment, net	11,251	12,627
Operating lease right-of-use assets	22,416	23,509
Long-term marketable securities	13,542	17,871
Restricted cash	1,446	1,446
Total assets	136,263	156,319
Current liabilities:
Accounts payable	1,898	2,558
Accrued compensation	2,613	5,355
Accrued and other current liabilities	8,884	6,550
Total current liabilities	13,395	14,463
Operating lease liability, net of current portion	32,036	34,468
Long-term debt, net	24,892	24,508
Other long-term liabilities	23	0
Total liabilities	70,346	73,439
Commitments and contingencies (Note 6)
Stockholders’ equity:
Convertible preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value; 300,000,000 shares authorized as of June 30, 2021 and December 31, 2020; 55,104,250 and 53,253,213 shares issued and outstanding as of June 30, 2021 and December 31, 2020, respectively	5	5
Additional paid-in capital	438,788	422,379
Related party promissory notes for purchase of common stock	0	(210)
Accumulated other comprehensive gain	5	5
Accumulated deficit	(372,881)	(339,299)
Total stockholders’ equity	65,917	82,880
Total liabilities and stockholders’ equity	$ 136,263	$ 156,319

Commitments and Contingencies - Summary of Supplemental Information Related to Leases (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Operating cash flows from operating leases	$ 3,313	$ 2,557
Operating leases, Weighted-average remaining lease term (years)	8 years 1 month 6 days	8 years 9 months 18 days
Operating leases, Weighted-average discount rate (percentage)	5.90%	5.80%

Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	At-the-Market Equity Offering Program	Common Stock	Common Stock At-the-Market Equity Offering Program	Additional Paid-In Capital	Additional Paid-In Capital At-the-Market Equity Offering Program	Related Party Promissory Notes for Purchase of Common Stock	Promissory Notes for Purchase of Common Stock	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit	Employee Promissory Notes for Purchase of Common Stock
Beginning balance at Dec. 31, 2019	$ 120,707		$ 5		$ 366,695		$ (210)		$ 90	$ (245,455)	$ (418)
Beginning balance, (in shares) at Dec. 31, 2019			47,227,065
Issuance of common stock, net of issuance costs, under at-the-market equity ("ATM") offering program		$ 8,763				$ 8,763
Issuance of common stock (in shares)				1,513,840
Issuance of common stock upon exercise of stock options	249				249
Issuance of common stock upon exercise of stock options (in shares)			73,049
Vesting of early exercised stock options	40				40
Stock-based compensation	3,225				3,225
Common stock issued for services	100				100
Common stock issued for services (in shares)			43,550
Unrealized gain (loss) on available-for-sale marketable securities	283								283
Net loss	(28,038)									(28,038)
Ending balance at Mar. 31, 2020	105,329		$ 5		379,072		(210)		373	(273,493)	(418)
Ending balance, (in shares) at Mar. 31, 2020			48,857,504
Beginning balance at Dec. 31, 2019	120,707		$ 5		366,695		(210)		90	(245,455)	(418)
Beginning balance, (in shares) at Dec. 31, 2019			47,227,065
Unrealized gain (loss) on available-for-sale marketable securities	142
Net loss	(46,705)
Ending balance at Jun. 30, 2020	112,259		$ 5		404,754		(210)		232	(292,160)	(362)
Ending balance, (in shares) at Jun. 30, 2020			51,729,511
Beginning balance at Dec. 31, 2019	120,707		$ 5		366,695		(210)		90	(245,455)	(418)
Beginning balance, (in shares) at Dec. 31, 2019			47,227,065
Ending balance at Dec. 31, 2020	$ 82,880		$ 5		422,379		(210)		5	(339,299)
Ending balance, (in shares) at Dec. 31, 2020	53,253,213		53,253,213
Beginning balance at Mar. 31, 2020	$ 105,329		$ 5		379,072		(210)		373	(273,493)	(418)
Beginning balance, (in shares) at Mar. 31, 2020			48,857,504
Issuance of common stock, net of issuance costs, under at-the-market equity ("ATM") offering program		20,731				20,731
Issuance of common stock (in shares)				2,594,030
Issuance of common stock upon exercise of stock options	355				355
Issuance of common stock upon exercise of stock options (in shares)			105,142
Issuance of common stock from restricted stock units, (in shares)			103,020
Vesting of early exercised stock options	132				132
Stock-based compensation	4,079				4,079
Issuance of common stock under 2018 ESPP	385				385
Issuance of common stock under 2018 ESPP (in Shares)			69,815
Repayment of promissory note for purchase of common stock	56										56
Unrealized gain (loss) on available-for-sale marketable securities	(141)								(141)
Net loss	(18,667)									(18,667)
Ending balance at Jun. 30, 2020	112,259		$ 5		404,754		(210)		232	(292,160)	$ (362)
Ending balance, (in shares) at Jun. 30, 2020			51,729,511
Beginning balance at Dec. 31, 2020	$ 82,880		$ 5		422,379		(210)		5	(339,299)
Beginning balance, (in shares) at Dec. 31, 2020	53,253,213		53,253,213
Issuance of common stock, net of issuance costs, under at-the-market equity ("ATM") offering program		$ 8,892				$ 8,892
Issuance of common stock (in shares)				1,220,629
Issuance of common stock upon exercise of stock options	$ 1,183				1,183
Issuance of common stock upon exercise of stock options (in shares)			259,019
Repurchase of early exercised shares, (in shares)			(33,370)
Stock-based compensation	2,744				2,744
Vesting of restricted stock units, (in shares)			88,218
Reclass of promissory notes for purchase of common stock							210	$ (210)
Unrealized gain (loss) on available-for-sale marketable securities	10								10
Net loss	(15,756)									(15,756)
Ending balance at Mar. 31, 2021	79,953		$ 5		435,198			(210)	15	(355,055)
Ending balance, (in shares) at Mar. 31, 2021			54,787,709
Beginning balance at Dec. 31, 2020	$ 82,880		$ 5		422,379		$ (210)		5	(339,299)
Beginning balance, (in shares) at Dec. 31, 2020	53,253,213		53,253,213
Issuance of common stock upon exercise of stock options (in shares)	430,047
Unrealized gain (loss) on available-for-sale marketable securities	$ 0
Net loss	(33,582)
Ending balance at Jun. 30, 2021	$ 65,917		$ 5		438,788				5	(372,881)
Ending balance, (in shares) at Jun. 30, 2021	55,104,250		55,104,250
Beginning balance at Mar. 31, 2021	$ 79,953		$ 5		435,198			(210)	15	(355,055)
Beginning balance, (in shares) at Mar. 31, 2021			54,787,709
Issuance of common stock upon exercise of stock options	612				612
Issuance of common stock upon exercise of stock options (in shares)			238,519
Stock-based compensation	2,782				2,782
Issuance of common stock under 2018 ESPP	196				196
Issuance of common stock under 2018 ESPP (in Shares)			54,943
Vesting of restricted stock units, (in shares)			23,079
Repayment of promissory note for purchase of common stock	210							$ 210
Unrealized gain (loss) on available-for-sale marketable securities	(10)								(10)
Net loss	(17,826)									(17,826)
Ending balance at Jun. 30, 2021	$ 65,917		$ 5		$ 438,788				$ 5	$ (372,881)
Ending balance, (in shares) at Jun. 30, 2021	55,104,250		55,104,250

Stock-Based Compensation - Summary of Restricted Stock Units, Performance Stock Units and Restricted Stock Awards Activity (Details) - RSU, RSA and PSU	6 Months Ended
	Jun. 30, 2021 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Unvested at December 31, 2020 \| shares	2,922,077
Shares, Granted \| shares	536,723
Shares, Vested \| shares	(111,297)
Shares, Canceled \| shares	(357,380)
Shares, Unvested at June 30, 2021 \| shares	2,990,123
Unvested at December 31, 2020 \| $ / shares	$ 3.44
Granted \| $ / shares	5.02
Vested \| $ / shares	6.58
Canceled \| $ / shares	3.35
Unvested at June 30, 2021 \| $ / shares	$ 3.62

Equity Financing

6 Months Ended

Jun. 30, 2021

Equity [Abstract]

Equity Financing

9. Equity Financing

In June 2019, the Company filed a Registration Statement on Form S-3 (the “Shelf Registration Statement”), covering the offering of up to $250.0 million of common stock, preferred stock, debt securities, warrants, and units. The Shelf Registration Statement included a prospectus covering the offering, issuance and sale of up to $75.0 million of the Company’s common stock from time to time through an “at-the-market” offering under the Securities Act of 1933, as amended (the “Initial ATM Offering Program”). The SEC declared the Shelf Registration Statement effective on June 6, 2019.

In June 2019, the Company also entered into a sales agreement (the “June 2019 Sales Agreement”) with Cowen and Company, LLC (“Cowen”) to sell shares of the Company’s common stock, from time to time, with aggregate gross sales proceeds of up to $75.0 million, through the ATM Offering Program under which Cowen acts as its sales agent. Cowen is entitled to compensation for its services equal to up to 3.0% of the gross proceeds of any shares of common stock sold through Cowen under the June 2019 Sales Agreement. During the year ended December 31, 2020, the Company issued and sold 5,002,257 shares of its common stock through its ATM Offering Program and received net proceeds of approximately $37.3 million, after deducting commissions and other offering expenses of $1.3 million.

In July 2020, the Company filed an additional prospectus supplement to the Shelf Registration Statement. This prospectus supplement covers the offering, issuance and sale of up to an additional $50.0 million of the Company’s common stock from time to time through an additional “at-the-market” offering under the Securities Act of 1933, as amended (the “Additional ATM Offering Program”). The Initial ATM Offering Program and Additional ATM Offering Program are collectively (the “ATM Offering Programs”).

In July 2020, the Company entered into a second sales agreement (the “July 2020 Sales Agreement”) with Cowen to sell shares of the Company’s common stock, from time to time, with aggregate gross sales proceeds of up to $50.0 million, through the Additional ATM Offering Program under which Cowen will act as its sales agent. The issuance and sale of shares of common stock by the Company pursuant to the July 2020 Sales Agreement are also deemed an “at-the-market” offering under the Securities Act of 1933, as amended (the “Securities Act”). Cowen is entitled to compensation for its services equal to up to 3.0% of the gross proceeds of any shares of common stock sold through Cowen under the July 2020 Sales Agreement. During the three months ended June 30, 2021, there were no shares of the Company’s common stock sold through either the Initial ATM Offering Program or the Additional ATM Offering Program. During the six months ended June 30, 2021, there were 1,187,068 shares of the Company’s common stock sold through the Initial ATM Offering Program and 33,561 shares of the Company’s common stock sold through the Additional ATM Offering Program and received total net proceeds of approximately $8.9 million, after deducting commissions and other offering expenses of $0.3 million.

Term Loan Facility - Schedule of Future Principal Payments for Long-Term Debt (Details) $ in Thousands	Jun. 30, 2021 USD ($)
Debt Disclosure [Abstract]
2021 (for the remaining 6 months)	$ 0
2022	3,838
2023	12,272
2024	8,890
Total principal payments	25,000
End of term fee due at maturity in 2024	1,562
Total principal and end of term fee payments	26,562
Unamortized discount and debt issuance costs	(1,670)
Long-term debt, net	$ 24,892

Marketable Securities - Additional Information (Details)	6 Months Ended
	Jun. 30, 2021 USD ($)
Marketable Securities [Line Items]
Realized gains or losses on available-for-sale debt securities	$ 0
Maximum
Marketable Securities [Line Items]
Available-for sale securities, remaining contractual maturity	2 years

Commitments and Contingencies

6 Months Ended

Jun. 30, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

6. Commitments and Contingencies

Leases

In February 2019, the Company entered into a lease agreement for new office and laboratory space in South San Francisco, California. The term of the lease agreement commenced in May 2019. The lease has an initial term from occupancy of approximately ten years ending on December 31, 2029 with an option to extend the term for an additional eight years at then-market rental rates. The total base rent payment escalates annually based on a fixed percentage beginning from the 13^th month of the lease agreement. The Company will also be responsible for the operating expenses and real estate taxes allocated to the building and common areas. Pursuant to the lease agreement, the landlord provided the Company with a tenant improvement allowance of $10.7 million, which was included in deferred rent and leasehold improvements on the balance sheet at December 31, 2019. In connection with the execution of the lease agreement, the Company delivered a letter of credit of approximately $0.9 million to the landlord.

In May 2016, the Company executed a non-cancellable lease agreement for office and laboratory space in Brisbane, California which commenced in May 2016 and continues through October 2022. The lease agreement includes an escalation clause for increased rent and a renewal provision allowing the Company to extend this lease for an additional four years by giving the landlord written notice of the election to exercise the option at least fifteen months prior to the original expiration of the lease term. The lease provides for monthly base rent amounts escalating over the term of the lease and the lessor provided the Company a $3.9 million tenant improvement allowance to complete the laboratory and office renovation which was recorded as deferred rent liability and leasehold improvements within property and equipment, net. In May 2017, the Company entered into an amendment to expand the leased space and received a three-month rent holiday for the expanded space.

The Company’s operating leases include various covenants, indemnities, defaults, termination rights, security deposits and other provisions customary for lease transactions of this nature.

The following table summarizes the components of lease expense, which are included in operating expenses in the Company’s condensed statements of operations and comprehensive loss (in thousands):

	Three Months Ended June 30,					Six Months Ended June 30,
	2021			2020		2021			2020
Operating lease cost	$	1,091		$	1,144	$	2,187		$	2,444
Variable lease cost		387			363		853			641
Sublease income		(390	)		—		(535	)		—
Impairment of operating lease right-of-use asset		—			—		—			1,157
Total lease cost	$	1,088		$	1,507	$	2,505		$	4,242

Variable lease payments include amounts relating to common area maintenance, real estate taxes and insurance and are recognized in the condensed statements of operations and comprehensive loss as incurred.

The following table summarizes supplemental information related to leases (in thousands):

	Six Months Ended June 30,
	2021			2020
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$	3,313		$	2,557
Weighted-average remaining lease term (years)
Operating leases		8.1			8.8
Weighted-average discount rate (percentage)
Operating leases		5.9	%		5.8	%

The following table summarizes the maturities of lease liabilities as of June 30, 2021 (in thousands):

	Amount
2021 (remaining 6 months)	$	3,343
2022		6,283
2023		4,810
2024		4,964
2025		5,123
Thereafter		22,179
Total future minimum lease payments		46,702
Less: Amount representing interest		(9,930	)
Present value of future minimum lease payments		36,772
Less: Current portion of operating lease liability		(4,736	)
Noncurrent portion of operating lease liability	$	32,036

In February 2020, the Company completed its move into the new office and laboratory space in South San Francisco, exited its previous offices and laboratory space in Brisbane, California, and began to actively market this space for sublease. Concurrent with this move and in consideration of real estate market conditions, in particular due to the COVID-19 pandemic in March 2020, the Company identified indicators of impairment in the related asset group, which included the leased ROU asset and related leasehold improvements associated with the lease. The Company subsequently evaluated and compared the net book value of the asset group to the estimated undiscounted future cash flows over the remaining term of the lease and concluded that an impairment had occurred. The discounted estimated future cash flows included estimates of sublease rentals through the end of the lease term, which ends on October 31, 2022, utilizing a discount rate of 3.5% based on the Company’s estimated incremental borrowing rate at that time. The estimated discounted cash flows were compared to the net book value of the ROU asset and leasehold improvements resulting in an impairment loss of $2.2 million during the six months ended June 30, 2020, which was included in operating expense in the statements of operations and comprehensive loss. No impairment loss was recorded during the three and six months ended June 30, 2021.

In February 2021, the Company entered into an agreement to sublease the first floor of the Brisbane, California facility, consisting of approximately 27,000 square feet, to Zymergen, Inc., through August 31, 2022. The base sublease rent rate is $3.53 per rental square foot per month and will increase by 3% on March 1, 2022 through expiration of the agreement. Additionally, the subtenant is required to pay approximately 41% of operating expenses and property management fees that the Company is required to pay under the lease for the Brisbane, California facility. In May 2021, the Company entered into an agreement to sublease the second floor of the Brisbane, California facility, consisting of approximately 11,500 square feet, to CareDx, Inc., through September 30, 2022. The base sublease rent rate is $1.00 per rental square foot per month through expiration of the agreement. Additionally, the subtenant is required to pay approximately 30% of operating expenses and property management fees that the Company is required to pay under the lease for the Brisbane, California facility. The Company incurred initial direct costs of $0.1 million in sublease commissions related to entering into the agreements to sublease the Brisbane, California facility. To account for the commissions, the Company capitalized the total commissions amount and will amortize the balance over the term of the sublease. Sublease income was $0.4 million and $0.5 million for the three and six months ended June 30, 2021, respectively.

In June 2021, the Company entered into an agreement to sublease a portion of the first floor of the South San Francisco, California facility, consisting of approximately 23,000 square feet, to Freenome Holdings, Inc., through August 31, 2024. The base sublease rent rate is $6.25 per rental square foot per month and will increase annually by 3.5% through expiration of the agreement. Additionally, the subtenant is required to pay approximately 37% of operating expenses and property management fees that the Company is required to pay under the lease for the South San Francisco, California facility. No impairment loss was recorded during the three and six months ended June 30, 2021.

Indemnifications

The Company indemnifies each of its officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the Company’s request in such capacity, as permitted under Delaware law and in accordance with the Company’s amended and restated certificate of incorporation and bylaws.

The term of the indemnification period lasts as long as an officer or director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity.

The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance. This insurance allows the transfer of risk associated with the Company’s exposure and may enable the Company to recover a portion of any future amounts paid. The Company believes that the fair value of these potential indemnification obligations is minimal. Accordingly, the Company has not recognized any liabilities relating to these obligations for any period presented.