Capitalized Software, Furniture, Equipment and Leasehold Improvements - Capitalized Software Development Costs, Furniture, Equipment and Leasehold Improvements, Net of Accumulated Depreciation and Amortization (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	$ 183,639	$ 140,012
Accumulated depreciation and amortization	(120,629)	(101,464)
Furniture, equipment, leasehold improvements and capitalized software, net of accumulated depreciation and amortization	63,010	38,548
Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	97,113	86,129
Computer Hardware and Related Software [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	42,705	35,945
Office Hardware [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	5,909	4,575
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	5,385	2,347
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	$ 32,527	$ 11,016