Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Commitments and Contingencies [Line Items]
Total deferred rent obligation	$ 0.1		$ 0.1		$ 0.3
Rent expense of office facilities and real estate	2.0	1.7	6.2	5.7
Rent expense for telecommunications and other equipment	1.5	1.8	4.6	5.3
Outstanding letter of credit	$ 1.1		$ 1.1
Maximum [Member]
Commitments and Contingencies [Line Items]
Outstanding letter of credit, maturity term			3 months