Property and Equipment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 529,667		$ 480,237
Less: Accumulated depreciation	(262,213)		(235,113)
Total property and equipment, net	267,454		245,124	[1]
Depreciation	27,700	$ 20,400
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	360,506		326,378
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	48,108		46,413
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	63,082		56,232
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	39,844		38,789
Building
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,044		7,084
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 11,083		$ 5,341

[1] As adjusted to reflect the impact of the full retrospective adoption of Topic 606. See Note 2 for further details.