Income Taxes (Details 1) (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
Effective Income Tax Rate Reconciliation
Computed expected income tax expense									$ 54,831,000	$ 30,749,000	$ 48,657,000
State income tax expense									4,122,000	2,441,000	3,478,000
Domestic Production Activity Deduction									(2,695,000)	(1,190,000)	(595,000)
Settlements of tax matters										(2,972,000)
Other									671,000	870,000	574,000
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
Effective income tax rate									36.30%	34.00%	37.50%