Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2011	Sep. 30, 2012	Sep. 30, 2011
Current portion of income tax expense:
Federal	$ 0	$ (20,699)		$ 0	$ (29,855)
State	(174)	(637)		(435)	(1,036)
Deferred portion of income tax expense	22,910	(112,010)		(7,305)	(164,251)
Income tax benefit (expense)	22,736	(133,346)		(7,740)	(195,142)
Effective tax rate (as a percent)	37.20%	36.70%		37.50%	36.70%
Amount of refund received from net operating loss carryback claim			$ 5,500