Stock-based Compensation Employee Service Share-based Compensation, Allocation of Costs (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 7,200	$ 9,900	$ 20,879	$ 34,194	$ 22,942
Cost of services and sales, exclusive of depreciation [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation			7,288	8,648	8,879
General and Adminstrative Expense, exclusive of depreciation [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation			$ 13,591	$ 25,546	$ 14,063