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Commitments and Contingencies - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Commitments and Contingencies [Line Items]      
Rent expense of office facilities and real estate $ 8.1 $ 8.2 $ 7.7
Rent expense for telecommunications and other equipment 5.4 $ 6.1 $ 7.0
Outstanding letter of credit $ 0.9    
Maximum [Member]      
Commitments and Contingencies [Line Items]      
Outstanding letter of credit, maturity term 3 months