Basis of Presentation and Significant Accounting Policies (Recently Issued Accounting Literature) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to retained earnings	$ (4,183,253)	$ (1,419,382)
Net cash provided by operating activities	860,142	995,080	$ 672,091
Net cash used in investing activities	(206,317)	(893,110)	(732,424)
Net cash (used in) provided by financing activities	$ (338,344)	(446,154)	618,859
Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to retained earnings				$ 109,553
Accounting Standards Update 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		(2,668)	1,801
Net cash used in investing activities		$ (2,668)	(13,199)
Net cash (used in) provided by financing activities			$ (15,000)