Income Taxes (Components of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current tax expense (benefit):
U.S. federal	$ 2,524,458	$ 76,175	$ (8,499)
State and local	0	0	0
Total	2,524,458	76,175	(8,499)
Deferred tax expense (benefit):
U.S. federal	(3,204,951)	(84,460)	17,103
State and local	0	0	0
Total	(3,204,951)	(84,460)	17,103
Total income tax expense (benefit)	(680,493)	(8,285)	8,604
Total income tax expense (benefit) reported in equity related to:
Other comprehensive income (loss)	(194,446)	(20,708)	7,407
Additional paid-in capital	(9,531)	0	0
Total income tax expense (benefit)	$ (884,470)	$ (28,993)	$ 16,011