CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $)	Preferred Stock [Member]	Common Stock [Member]	Common Stock Warrants [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [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	245,229	0	1,455,969	0	0	1,701,198
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits (in shares)		245,229
Repurchase of preferred stock	(71,250,000)	0	0	0	0	0	(71,250,000)
Stock Repurchased During Period, Shares		0
Issuance of restricted common shares, net of forfeitures	0	102,119	0	(102,119)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)		102,119
Issuance of salary stock units	0	57,508	0	942,565	0	0	1,000,073
Issuance of salary stock units (in shares)		57,508
Restricted shares withheld for taxes	0	(63,219)	0	(1,021,409)	0	0	(1,084,628)
Restricted shares withheld for taxes (in shares)		(63,219)
Compensation expense for restricted shares	0	0	0	3,270,028	0	0	3,270,028
Compensation expense for stock options	0	0	0	394,466	0	0	394,466
Common dividends paid							0
Accretion on preferred stock discount	2,153,172	0	0	0	(2,153,172)	0	0
Preferred dividends paid	0	0	0	0	(2,127,604)	0	(2,127,604)
Net income (loss)	0	0	0	0	41,883,881	0	41,883,881
Other comprehensive income (loss)						(4,105,623)	(4,105,623)
Ending 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	280,008	0	3,961,042	0	0	4,241,050
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits (in shares)		280,008
Issuance of restricted common shares, net of forfeitures	0	303,111	0	(303,111)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)		303,111
Restricted shares withheld for taxes	0	(57,775)	0	(1,288,367)	0	0	(1,346,142)
Restricted shares withheld for taxes (in shares)		(57,775)
Compensation expense for restricted shares	0	0	0	4,069,662	0	0	4,069,662
Compensation expense for stock options	0	0	0	12,470	0	0	12,470
Common dividends paid					(2,814,691)		(2,814,691)
Cancellation of outstanding warrants	0	0	(3,348,402)	2,593,402	0	0	(755,000)
Net income (loss)					57,726,201		57,726,201
Other comprehensive income (loss)	0	0	0	0	0	(17,252,248)	(17,252,248)
Ending Balances at Dec. 31, 2013	0	35,221,941	0	550,212,135	142,298,199	(4,024,614)	723,707,661
Balances (in shares) at Dec. 31, 2013		35,221,941
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits	0	302,403	0	8,444,894	0	0	8,747,297
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits (in shares)		302,403
Issuance of restricted common shares, net of forfeitures	0	277,187	0	(277,187)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)		277,187
Restricted shares withheld for taxes	0	(69,048)	0	(2,256,560)	0	0	(2,325,608)
Restricted shares withheld for taxes (in shares)		(69,048)
Compensation expense for restricted shares	0	0	0	5,308,167	0	0	5,308,167
Common dividends paid	0	0	0	0	(11,398,285)	0	(11,398,285)
Net income (loss)	0	0	0	0	70,471,167	0	70,471,167
Other comprehensive income (loss)	0	0	0	0	0	8,182,982	8,182,982
Ending Balances at Dec. 31, 2014		$ 35,732,483	$ 0	$ 561,431,449	$ 201,371,081	$ 4,158,368	$ 802,693,381
Balances (in shares) at Dec. 31, 2014		35,732,483