Commitments and Contingencies - Additional Information (Detail)		1 Months Ended			12 Months Ended
	Nov. 01, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Nov. 30, 2011 USD ($)	Dec. 31, 2021 USD ($) Claim	Dec. 31, 2020 USD ($)	May 31, 2021 USD ($)	Jan. 01, 2021 USD ($)
Gain Contingencies [Line Items]
Sublease Income					$ 100,000
Aggregate sublease payment receivable	$ 3,400,000
Operating lease right-of-use assets					20,333,000
Lease liabilities					$ 34,589,000
Weighted average incremental borrowing rate					8.40%
Operating lease cost					$ 2,900,000
Variable lease payments					400,000
Rent expense						$ 400,000
Income (loss)					(130,323,000)	(63,412,000)
Loss contingency accrual					$ 0
Indemnification Agreement [Member]
Gain Contingencies [Line Items]
Loss contingency pending claims | Claim					0
Stanford Agreement [Member] | Research and Development Arrangement [Member]
Gain Contingencies [Line Items]
Sponsor research agreements, commitment amount				$ 500,000
Sponsored Research Agreement [Member]
Gain Contingencies [Line Items]
Maximum threshold period allowed for filing market authorization			15 years
Proceeds from funding					$ 135,000
Income (loss)						$ 0
Sponsored Research Agreement [Member] | Other Income [Member]
Gain Contingencies [Line Items]
Proceeds from funding					$ 590,000
Sponsored Research Agreement [Member] | Research and Development Arrangement [Member]
Gain Contingencies [Line Items]
Maximum expected research funding			$ 651,000
South San Francisco, California [Member]
Gain Contingencies [Line Items]
Operating lease, term of contract					7 years
Operating lease, expiration month and year					2024-06
Operating lease, renewal term					5 years
Brisbane, California [Member]
Gain Contingencies [Line Items]
Operating lease, term of contract		10 years				10 years
Operating lease, renewal term		10 years				10 years
Operating lease, expected to begin month and year		2021-11
Operating lease, option to extend [true false]		true
Operating lease, base rent abatement period		3 months
Tenant improvement allowance receivable		$ 10,800,000				$ 10,800,000
Letter of credit		$ 1,000,000.0				$ 1,000,000.0
Operating lease consideration allocated recorded as liability								$ 1,300,000
Operating lease right-of-use assets					$ 20,300,000		$ 21,000,000.0
Lease liabilities					$ 34,600,000		$ 22,200,000
Weighted average remaining lease term					9 years 10 months 24 days
Operating lease, commenced month and year		2021-05