Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Commitments and Contingencies [Line Items]
Rent expense of office facilities and real estate	$ 2.1	$ 2.1	$ 4.1	$ 4.1
Rent expense for telecommunications and other equipment	1.3	$ 1.6	2.6	$ 3.0
Outstanding letter of credit	$ 0.9		$ 0.9
Maximum [Member]
Commitments and Contingencies [Line Items]
Outstanding letter of credit, maturity term			3 months