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Commitments and Contingencies - Additional Information (Detail)
$ in Thousands
 1 Months Ended 12 Months Ended
Jan. 31, 2018
Dec. 31, 2017
USD ($)
ft²
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Commitments and Contingencies [Line Items]        
Transition tax   $ 40,250    
Total rental expenses under operating lease agreements   $ 19,800 $ 20,300 $ 22,600
Date of dismissal   Oct. 20, 2017    
Other Long-term Liabilities        
Commitments and Contingencies [Line Items]        
Transition tax   $ 36,800    
Prepaid Expenses and Other Current Assets        
Commitments and Contingencies [Line Items]        
Transition tax   $ 3,500    
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   $ 8,500 12,300  
Deferred rent included in current accrued expenses   $ 3,800 $ 3,500  
Northern Virginia Office Space | Subsequent Event        
Commitments and Contingencies [Line Items]        
Lease expiration date 2030-12