Nature of Business and Summary of Significant Accounting Policies - Net Property and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 190,121	$ 182,762
Less: accumulated depreciation	(117,392)	(102,534)
Property and equipment, net	72,729	80,228
Computer and office equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 129,359	123,804
Computer and office equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	3 years
Computer and office equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	5 years
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Useful Lives, description	Lesser of useful life of improvement or remaining life of lease
Property and equipment, gross	$ 32,096	32,364
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	7 years
Property and equipment, gross	$ 12,500	12,158
Building and improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 14,381	12,651
Building and improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	7 years
Building and improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	30 years
Land [Member]
Property, Plant and Equipment [Line Items]
Useful Lives, description	Non depreciable
Property and equipment, gross	$ 1,785	$ 1,785