Leases - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Operating Leased Assets [Line Items]
Operating lease, right of use asset	$ 79,296		$ 85,538
Right of use asset obtained in exchange for operating lease liability	700	$ 5,000
UNITED STATES
Operating Leased Assets [Line Items]
Operating lease, right of use asset	67,600		71,000
Operating lease, liability	93,100		97,500
UNITED STATES | Northern Virginia Office Space
Operating Leased Assets [Line Items]
Operating lease, right of use asset	64,100		66,900
Operating lease, liability	89,600		93,300
Non-US
Operating Leased Assets [Line Items]
Operating lease, right of use asset	11,700		14,500
Operating lease, liability	$ 12,600		$ 15,500