Income Taxes (Components of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current tax expense (benefit):
U.S. Federal	$ 105,992	$ 112,742	$ 250,601
State and local	129	0	0
Total	106,121	112,742	250,601
Deferred tax expense (benefit):
U.S. Federal	(114,126)	27,631	315,819
Total	(114,126)	27,631	315,819
Total income tax expense (benefit)	(8,005)	140,373	566,420
Total income tax expense (benefit) reported in equity related to:
Other comprehensive income (loss)	(61,322)	65,717	(113,517)
Additional paid-in capital	(6,560)	(6,507)	(7,574)
Total income tax expense (benefit)	$ (75,887)	$ 199,583	$ 445,329