Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current:
U.S. federal and state - current									$ 6,464	$ 4,763	$ 8,830
Current tax benefit on equity compensation									6,212	17,522	14,213
Total current tax									12,676	22,285	23,043
Deferred:
U.S. federal and state - deferred									244,994	236,330	(268,179)
Total income tax(benefit) provision	$ 74,279	$ 81,713	$ 57,709	$ 43,969	$ 20,139	$ 88,059	$ 34,145	$ 116,272	$ 257,670	$ 258,615	$ (245,136)