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Commitments and Contingencies - Additional Information (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2015
USD ($)
ft²
Dec. 31, 2014
USD ($)
ft²
Dec. 31, 2013
USD ($)
Commitments and Contingencies [Line Items]      
Total rental expenses under operating lease agreements $ 22.6 $ 30.4 $ 28.3
Northern Virginia Office Space      
Commitments and Contingencies [Line Items]      
Office space area leased under the agreement | ft² 214,000 233,000  
Lease expiration date 2020-12    
Deferred rent included in other long-term liabilities $ 15.7 $ 18.9  
Deferred rent included in current accrued expenses $ 3.3 $ 3.0  
Northern Virginia Office, Additional Office Space | 2014 Restructuring Plan      
Commitments and Contingencies [Line Items]      
Lease expiration date 2015-02    
Office space ceased to be used | ft² 19,000