Leases - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Restricted cash	$ 999	$ 999
Operating lease right-of-use assets	19,376	20,963
Lease liability	30,708
Rent expense	5,800	6,500	$ 3,300
Variable lease costs	$ 1,500	$ 1,600
ASU No. 2016-2, Leases
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets				$ 23,100
Lease liability				$ 24,700
Estimated incremental borrowing rate				8.50%
Redwood City
Lessee, Lease, Description [Line Items]
Lease term	10 years
Lease renewal term	7 years
Lease incentive allowance	$ 8,100
Restricted cash	$ 1,000