Supplemental Consolidated Balance Sheet Information (Property and Equipment, Net) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 191,879	$ 188,941
Less: accumulated depreciation and amortization	(130,505)	(125,916)
Property and equipment, net	61,374	63,025
Furniture, Fixtures and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	56,944	55,619
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	87,821	86,225
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 47,114	$ 47,097