Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Commitments and Contingencies [Line Items]
Total rental expenses under operating lease agreements	$ 20.3	$ 22.6	$ 30.4
Northern Virginia Office Space
Commitments and Contingencies [Line Items]
Office space area leased under the agreement | ft²	214,000
Lease expiration date	2020-12
Deferred rent included in other long-term liabilities	$ 12.3	15.7
Deferred rent included in current accrued expenses	$ 3.5	$ 3.3