CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) (USD $)	Preferred Stock [Member]	Common Stock [Member]	Common Stock Warrants [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comp. Income, Net [Member]	Total
Balances at Dec. 31, 2011	$ 69,096,828	$ 34,354,960	$ 3,348,402	$ 536,227,537	$ 49,783,584	$ 17,333,257	$ 710,144,568
Balances (in shares) at Dec. 31, 2011		34,354,960
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits	0	180,487	0	304,428	0	0	484,915
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits (in shares)		180,487
Issuance of restricted common shares, net of forfeitures		95,912	0	(95,912)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)		95,912
Issuance of salary stock units	0	27,672	0	449,891	0	0	477,563
Issuance of salary stock units (in shares)		27,672
Restricted shares withheld for taxes	0	(43,018)	0	(36,459)	0	0	(79,477)
Restricted shares withheld for taxes (in shares)		(43,018)
Compensation expense for restricted shares	0	0	0	857,160	0	0	857,160
Compensation expense for stock options	0	0	0	153,801	0	0	153,801
Accretion on preferred stock discount	258,647	0	0	0	(258,647)	0	0
Preferred dividends paid	0	0	0	0	(890,624)	0	(890,624)
Net income	0	0	0	0	8,364,954	0	8,364,954
Other comprehensive income	0	0	0	0	0	(847,412)	(847,412)
Ending Balances at Mar. 31, 2012	69,355,475	34,616,013	3,348,402	537,860,446	56,999,267	16,485,845	718,665,448
Balances (in shares) at Mar. 31, 2012		34,616,013
Balances at Dec. 31, 2012	0	34,696,597	0	543,760,439	87,386,689	13,227,634	679,071,359
Balances (in shares) at Dec. 31, 2012		34,696,597
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits	0	88,845	0	902,533	0	0	991,378
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits (in shares)		88,845
Issuance of restricted common shares, net of forfeitures	0	274,545	0	(274,545)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)		274,545
Restricted shares withheld for taxes	0	(37,500)	0	(731,679)	0	0	(769,179)
Restricted shares withheld for taxes (in shares)		(37,500)
Compensation expense for restricted shares	0	0	0	950,498	0	0	950,498
Compensation expense for stock options	0	0	0	12,471	0	0	12,471
Net income	0	0	0	0	13,448,125	0	13,448,125
Other comprehensive income	0	0	0	0	0	(2,270,910)	(2,270,910)
Ending Balances at Mar. 31, 2013	$ 0	$ 35,022,487	$ 0	$ 544,619,717	$ 100,834,814	$ 10,956,724	$ 691,433,742
Balances (in shares) at Mar. 31, 2013		35,022,487