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Commitments and Contingencies - Additional Information (Detail)
$ in Thousands
 1 Months Ended 3 Months Ended 12 Months Ended
Jan. 31, 2018
Sep. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
ft²
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Commitments and Contingencies [Line Items]          
Provision for transition tax     $ 37,200 $ 40,300  
Transition tax     28,935    
Measurement period adjustment to reduce transition tax   $ 3,100 3,100    
Total rental expenses under operating lease agreements     18,900 19,800 $ 20,300
Other Long-term Liabilities          
Commitments and Contingencies [Line Items]          
Transition tax     $ 28,900 36,800  
Northern Virginia Office Space          
Commitments and Contingencies [Line Items]          
Office space area leased under the agreement | ft²     214,000    
Lease expiration date 2030-12        
Northern Virginia Office Space | Other Long-term Liabilities          
Commitments and Contingencies [Line Items]          
Deferred rent included in other long-term liabilities     $ 26,900 $ 8,500