Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current
Federal	$ 60,253,000	$ 80,707,000	$ 12,381,000
State	26,260,000	31,792,000	(16,425,000)
Total	86,513,000	112,499,000	(4,044,000)
Deferred
Federal	9,525,000	(26,635,000)	20,125,000
State	2,784,000	(8,303,000)	9,974,000
Total	12,309,000	(34,938,000)	30,099,000
Income tax expense (benefit)
Federal	69,778,000	54,072,000	32,506,000
State	29,044,000	23,489,000	(6,451,000)
Income tax expense	98,822,000	77,561,000	26,055,000
Effective tax provision (benefit) (as a percent)	32.10%	30.60%	16.20%
Income taxes receivable	$ 59,600,000	$ 40,300,000