Income Taxes (Provision) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current tax expense:
Federal	$ 257,900	$ 87,700	$ 79,000
State	21,900	(15,000)	12,500
Total current tax expense	279,800	72,700	91,500
Deferred tax expense (benefit):
Federal	(32,100)	2,400	15,000
State	21,200	(19,000)	(6,400)
Total deferred tax expense (benefit)	(10,894)	(16,564)	8,645
Interest expense, gross of related tax effects	100	(1,900)	(300)
Total income tax provision	$ 268,967	$ 54,163	$ 99,827