Income Taxes Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
U.S. Federal									$ 65,856	$ (76,447)	$ 49,435
U.S. State									2,732	(1,924)	2,591
Non-U.S.									2,030	1,411	963
Current income tax expense (benefit)									70,618	(76,960)	52,989
Deferred:
U.S. Federal									17,397	89,268	66,187
U.S. State									(787)	2,257	6,429
Deferred income tax expense (benefit)									16,610	91,525	72,616
Income Tax Expense / Effective Rate	$ 64,441	$ 3,770	$ 9,611	$ 9,406	$ 14,824	$ (66)	$ (109)	$ (84)	$ 87,228	$ 14,565	$ 125,605