Leases - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Operating Leased Assets [Line Items]
Operating lease, right of use asset	$ 68,755		$ 73,597
Right of use asset obtained in exchange for operating lease liability	2,400	$ 700
UNITED STATES
Operating Leased Assets [Line Items]
Operating lease, right of use asset	58,600		62,200
Operating lease, liability	77,600		82,900
UNITED STATES | Northern Virginia Office Space
Operating Leased Assets [Line Items]
Operating lease, right of use asset	56,200		59,000
Operating lease, liability	75,200		79,700
Non-US
Operating Leased Assets [Line Items]
Operating lease, right of use asset	10,200		11,400
Operating lease, liability	$ 11,100		$ 12,200