Revenue (Breakdown of Revenues by Accounting Standards) (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	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customers									$ 898,885
Total Revenues	$ 812,662	$ 685,579	$ 911,402	$ 635,739	$ 1,004,072	$ 836,595	$ 993,662	$ 852,016	3,045,382	$ 3,686,345	$ 3,924,790
Revenues under ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customers									898,885
Revenues under ASC 840
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenues									105,631
Revenues under ASC 815
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenues									$ 2,040,866