Summary of Significant Accounting Policies (Cumulative Effect of the Changes Made to the Statement of Cash Flows for the Adoption of the New Revenue Standard) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 377,047	$ 263,269	$ 222,054
Adjustments to reconcile net income to net cash provided by operating activities:
Benefit of deferred income taxes	1,209	$ (7,918)	$ 20,881
All other adjustments to reconcile net income to net cash provided by operating activities	113,468
Changes in assets and liabilities, net	(91,640)
Net cash provided by operating activities	400,084
Previous U.S. GAAP
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	358,921
Adjustments to reconcile net income to net cash provided by operating activities:
Benefit of deferred income taxes	3,482
All other adjustments to reconcile net income to net cash provided by operating activities	113,468
Changes in assets and liabilities, net	(75,787)
Net cash provided by operating activities	400,084
Accounting Standards Update 2014-09 | Attributed to the New Revenue Standard
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	18,126
Adjustments to reconcile net income to net cash provided by operating activities:
Benefit of deferred income taxes	(2,273)
All other adjustments to reconcile net income to net cash provided by operating activities	0
Changes in assets and liabilities, net	(15,853)
Net cash provided by operating activities	$ 0