Revenue (Breakdown of Revenues by Accounting Standards) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customers	$ 156,394		$ 706,927
Total Revenues	685,579	$ 836,595	2,232,720	$ 2,682,273
Revenues under ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customers	156,394		706,927
Revenues under ASC 840
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenues	25,853		78,110
Revenues under ASC 815
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenues	$ 503,332		$ 1,447,683