Property and Equipment, net - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 47,811	$ 49,748
Less: Accumulated depreciation	(37,397)	(35,618)
Property, Plant and Equipment, Net	10,414	14,130
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,214	3,925
Computer And Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	36,835	34,895
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 7,762	$ 10,928