Income Taxes (Components of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current tax expense (benefit):
U.S. federal	$ 14,381	$ (422,999)	$ 501,088
State and local	0	0	1,349
Total	14,381	(422,999)	502,437
Deferred tax expense (benefit):
U.S. federal	(305,482)	584,503	698,662
State and local	0	0	0
Total	(305,482)	584,503	698,662
Total income tax expense (benefit)	(291,101)	161,504	1,201,099
Total income tax expense (benefit) reported in equity related to:
Other comprehensive income (loss)	200,447	(52,510)	98,644
Additional paid-in capital	0	0	0
Total income tax expense (benefit)	$ (90,654)	$ 108,994	$ 1,299,743