Fixed Assets, Net - Components of Fixed Assets, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Fixed assets, gross	$ 543,621	$ 462,270
Less: accumulated depreciation and amortization	(348,241)	(305,101)
Fixed assets, net	195,380	157,169
Computer and Communications Equipment [Member]
Property, Plant and Equipment [Line Items]
Fixed assets, gross	154,421	140,451
Software, Including Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Fixed assets, gross	234,564	194,470
Leasehold Improvements and Other Fixed Assets [Member]
Property, Plant and Equipment [Line Items]
Fixed assets, gross	$ 154,636	$ 127,349

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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