Composition of Certain Balance Sheet Accounts - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 161,350	$ 162,882
Accumulated depreciation	(102,143)	(99,389)
Total property and equipment, net	59,207	63,493
Office Equipment, Furniture, Fixtures and Other [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	11,786	10,986
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	12,012	12,012
Network Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 137,552	$ 139,884