Income Taxes (Schedule of Components of Income Tax Expense (Benefit) ) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Current income tax expense	$ 269,387	$ 153,176	$ 6,391
Deferred income tax expense (benefit)	(139,948)	50,951	(103,338)
Total income tax expense (benefit)	$ 129,439	$ 204,127	$ (96,947)