Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Abstract]
Unrecognized tax benefits	$ 0
Accrued interest	0
Accrued penalties	0
Current tax expense (benefit) [Abstract]
Federal	19,096,000	8,157,000	(13,412,000)
State	0	0	0
Total current tax expense (benefit)	19,096,000	8,157,000	(13,412,000)
Deferred tax expense (benefit) [Abstract]
Federal	485,000	(19,646,000)	13,482,000
State	1,063,000	(3,749,000)	4,340,000
Total deferred tax expense (benefit)	1,547,626	(23,395,052)	17,822,071
Income tax expense (benefit)	20,643,517	(15,237,687)	4,410,158
Federal income tax statutory rate (in hundredths)	35.00%
Reconciliation of the differences in income tax (benefit) expense [Abstract]
Income tax expense (benefit) at statutory rate	21,885,000	9,975,000	(6,962,000)
State excise tax expense (benefit), net of federal tax effect	1,063,000	(255,000)	(2,305,000)
Tax-exempt securities	(2,517,000)	(2,655,000)	(3,017,000)
Federal tax credits	0	0	(360,000)
Bank owned life insurance	(322,000)	(406,000)	(320,000)
Insurance premiums	(243,000)	(151,000)	(301,000)
Other items	778,000	734,000	600,000
Deferred tax valuation allowance	0	(22,480,000)	17,075,000
Income tax expense (benefit)	20,643,517	(15,237,687)	4,410,158
Deferred tax assets [Abstract]
Loan loss allowance	26,777,000	28,684,000
Loans	423,000	783,000
Insurance	691,000	664,000
Accrued liability for supplemental retirement agreements	510,000	476,000
Restricted stock and stock options	3,777,000	3,525,000
Net operating loss carryforward	3,593,000	4,753,000
Alternative minimum tax carryforward	0	3,341,000
Other real estate owned	3,222,000	2,076,000
Other deferred tax assets	1,430,000	1,152,000
Total deferred tax assets	40,423,000	45,454,000
Deferred tax liabilities [Abstract]
Depreciation and amortization	7,110,000	7,522,000
Core deposit intangible asset	1,700,000	2,735,000
Securities	12,024,000	14,675,000
REIT dividends	371,000	1,179,000
FHLB related liabilities	1,724,000	3,016,000
Other deferred tax liabilities	554,000	489,000
Total deferred tax liabilities	23,483,000	29,616,000
Net deferred tax assets	$ 16,940,000	$ 15,838,000
Cumulative pre-tax loss position period	3 years