Stock Based Compensation Schedule of compensation cost for share-based payment arrangements, allocation of share-based compensation costs by plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation	$ 33,519	$ 30,631	$ 16,052
Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation	28,027	24,899	11,049
PerformanceStock​Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation	$ 748	$ 1,707	$ 1,305