Fixed Assets, Net - Components of Fixed Assets, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Fixed assets, gross	$ 420,663	$ 361,069
Less: accumulated depreciation and amortization	274,790	249,049
Fixed assets, net	145,873	112,020
Computer and Communications Equipment [Member]
Property, Plant and Equipment [Line Items]
Fixed assets, gross	142,511	151,808
Software, Including Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Fixed assets, gross	140,416	103,872
Leasehold Improvements and Other Fixed Assets [Member]
Property, Plant and Equipment [Line Items]
Fixed assets, gross	$ 137,736	$ 105,389