Income Taxes (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income taxes currently payable:
Federal									$ 37,691,000	$ 18,345,000	$ 51,195,000
State									3,445,000	2,187,000	5,534,000
Aggregate income taxes currently payable									41,136,000	20,532,000	56,729,000
Deferred income taxes (benefits):
Federal									(1,726,000)	14,922,000	8,644,000
State									514,000	2,384,000	(336,000)
Aggregate deferred income taxes									(1,212,000)	17,306,000	8,308,000
Total income tax expense	9,888,000	(10,660,000)	21,586,000	19,110,000	21,418,000	(16,725,000)	18,611,000	14,534,000	39,924,000	37,838,000	65,037,000
Statutory federal income tax rate (as a percent)									35.00%	35.00%	35.00%
Differences between total income tax expense and amount computed using the statutory federal income tax rate
Income tax expense at federal statutory rate									57,815,000	67,107,000	68,458,000
State income taxes, net of federal income tax benefit									4,412,000	6,812,000	7,013,000
Tax contingencies reversed due to statute closings									(25,299,000)	(37,093,000)	(12,521,000)
Other-net									2,996,000	1,012,000	2,087,000
Total income tax expense	9,888,000	(10,660,000)	21,586,000	19,110,000	21,418,000	(16,725,000)	18,611,000	14,534,000	39,924,000	37,838,000	65,037,000
Deferred tax assets:
Operating loss carryforwards	8,604,000				10,116,000				8,604,000	10,116,000
Share-based compensation	15,926,000				16,225,000				15,926,000	16,225,000
Other accrued compensation	7,619,000				3,891,000				7,619,000	3,891,000
Community reinvestment reserves	550,000				6,276,000				550,000	6,276,000
Claims reserves	8,005,000				7,244,000				8,005,000	7,244,000
Deferred Revenue	6,708,000				2,408,000				6,708,000	2,408,000
Other non-deductible accrued liabilities	13,018,000				8,082,000				13,018,000	8,082,000
Indirect tax benefits	4,804,000				5,897,000				4,804,000	5,897,000
Other deferred tax assets	987,000				1,282,000				987,000	1,282,000
Total deferred tax assets	66,221,000				61,421,000				66,221,000	61,421,000
Valuation allowance	(3,102,000)				(3,130,000)				(3,102,000)	(3,130,000)
Deferred tax assets after valuation allowance	63,119,000				58,291,000				63,119,000	58,291,000
Deferred tax liabilities:
Depreciation	(43,417,000)				(44,728,000)				(43,417,000)	(44,728,000)
Amortization of goodwill and intangible assets	(20,615,000)				(15,782,000)				(20,615,000)	(15,782,000)
Other deferred tax liabilities	(3,603,000)				(169,000)				(3,603,000)	(169,000)
Total deferred tax liabilities	(67,635,000)				(60,679,000)				(67,635,000)	(60,679,000)
Net deferred tax assets (liabilities)	(4,516,000)				(2,388,000)				(4,516,000)	(2,388,000)
Federal
Income Taxes
Operating Loss Carryforwards	3,600,000								3,600,000
State
Income Taxes
Operating Loss Carryforwards	$ 152,300,000								$ 152,300,000