Leases - Additional Information (Detail) $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2021 USD ($) ft²	Sep. 30, 2021 USD ($)	Jun. 30, 2021 ft²	Aug. 31, 2021 ft²
Office Lease Agreement [Member]
Lessee Lease Description [Line Items]
Land subject to ground leases | ft²	62,000		62,000
Lease term of contract	11 years		11 years
Operating lease, existence of option to extend			true
Operating lease, renewal term	10 years		10 years
Operating lease, expense | $	$ 3.0
Office Lease Agreement [Member] | First Option To Extend Lease [Member]
Lessee Lease Description [Line Items]
Operating lease, renewal term	5 years		5 years
Office Lease Agreement [Member] | Second Option To Extend Lease [Member]
Lessee Lease Description [Line Items]
Operating lease, renewal term	5 years		5 years
San Francisco Office Building [Member] | Forecast
Lessee Lease Description [Line Items]
Land subject to ground leases | ft²				185,000
San Francisco Office Building [Member] | Maximum [Member] | Forecast
Lessee Lease Description [Line Items]
Operating lease, impairment loss | $		$ 80.0