Income Taxes (Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Statutory federal income tax rate			35.00%	35.00%	35.00%
Income tax expense (benefit) at statutory federal income tax rate			$ (518,258)	$ 49,130	$ 75,671
State income taxes, net of federal income tax benefit			(14,112)	93	1,461
Impact of state law changes			(3,075)	(121)	(1,966)
Impact of state deferred tax revaluation on San Juan properties	$ 1,200	$ 8,400	(1,241)	(8,382)	0
401(k) stock dividend deduction			0	(232)	(449)
Other, net			1,681	240	(394)
Total income tax expense (benefit)			$ (535,005)	$ 40,728	$ 74,323
Effective income tax rate (%)			36.13%	29.01%	34.38%