Income Taxes (Schedule of Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal current	$ 38,535	$ 237	$ 32,090
State current	3,979	2,928	5,665
Foreign current	102	534	1,250
Current income tax expense (benefit), total	42,616	3,699	39,005
Federal deferred	(104,573)	42,895	33,912
State deferred	3,625	1,737	4,530
Deferred income tax expense (benefit), total	(100,948)	44,632	38,442
Total income tax expense (benefit)	$ (58,332)	$ 48,331	$ 77,447