Income Taxes (Components of Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Taxes estimated to be payable currently:
Federal	$ 3,972	$ 161,576	$ 23,342
State	758	72,379	2,516
Total current	4,730	233,955	25,858
Taxes deferred:
Federal	(513,187)	144,645	85,950
State	(26,548)	(34,447)	(2,300)
Total deferred	(539,735)	110,198	83,650
Total income tax expense (benefit)	$ (535,005)	$ 344,153	$ 109,508