Stock-based Compensation Employee Service Share-based Compensation, Allocation of Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based Compensation	$ 22,942	$ 22,079	$ 21,279
Cost of services and sales, exclusive of depreciation [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based Compensation	8,879	10,073	10,126
General and Adminstrative Expense, exclusive of depreciation [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based Compensation	$ 14,063	$ 12,006	$ 11,153