Income Taxes (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current:
Federal									$ 34,457,000	$ 18,906,000	$ (5,562,000)
State									5,190,000	2,877,000	1,920,000
Total current									39,647,000	21,783,000	(3,642,000)
Deferred
Federal									16,132,000	7,237,000	52,369,000
State									1,150,000	878,000	3,387,000
Total deferred									17,282,000	8,115,000	55,756,000
Total income tax expense	$ (19,629,000)	$ (14,148,000)	$ (14,917,000)	$ (8,235,000)	$ (16,716,000)	$ (4,520,000)	$ (9,402,000)	$ 740,000	$ 56,929	$ 29,898,000	$ 52,114,000