Property And Equipment (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Amortization and impairment	$ 10,772	$ 10,502	$ 10,191	$ 9,991	$ 9,858	$ 9,402	$ 9,393	$ 9,237	$ 3,700	$ 41,456	$ 37,890	$ 37,175
Software and software development costs
Property, Plant and Equipment [Line Items]
Capitalized software development costs										21,900	20,500	14,800
Amortization expense										16,000	12,100	15,200
Unamortized software development costs	40,300									40,300
Total depreciation expense and amortization of capitalized software development costs										30,000	23,500	$ 23,900
Computers and equipment
Property, Plant and Equipment [Line Items]
Capital leased assets	1,200				1,700					1,200	1,700
Capital leased assets accumulated depreciation	$ 800				$ 1,100					$ 800	$ 1,100