Property And Equipment (Schedule Of Property And Equipment) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 201,759	$ 175,831
Less accumulated depreciation and amortization	(124,707)	(107,089)
Property and equipment, net	77,052	68,742
Computers and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	26,803	22,702
Software and software development costs
Property, Plant and Equipment [Line Items]
Property and equipment, gross	137,986	120,278
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,089	7,754
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 28,881	$ 25,097