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	230,718	0	1,297,396	0	0	1,528,114
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits (in shares)		230,718
Stock Repurchased During Period, Value	(71,250,000)	0	0	0	0	0	(71,250,000)
Issuance of restricted common shares, net of forfeitures	0	95,890	0	(95,890)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)		95,890
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	(47,417)	0	(741,427)	0	0	(788,844)
Restricted shares withheld for taxes (in shares)		(47,417)
Compensation expense for restricted shares	0	0	0	2,489,334	0	0	2,489,334
Compensation expense for stock options	0	0	0	329,350	0	0	329,350
Cancellation Of Outstanding Warrants	0	0	(3,348,402)	2,593,402	0	0	(755,000)
Accretion on preferred stock discount	2,153,172	0	0	0	(2,153,172)	0	0
Preferred dividends paid	0	0	0	0	(2,127,605)	0	(2,127,605)
Net income	0	0	0	0	30,153,723	0	30,153,723
Other comprehensive income	0	0	0	0	0	2,100,758	2,100,758
Ending Balances at Sep. 30, 2012	0	34,691,659	0	543,042,267	75,656,530	19,434,015	672,824,471
Balances (in shares) at Sep. 30, 2012		34,691,659
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	191,928	0	2,372,601	0	0	2,564,529
Exercise of employee common stock options, stock appreciation rights, common stock warrants and related tax benefits (in shares)		191,928
Issuance of restricted common shares, net of forfeitures	0	300,718	0	(300,718)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)		300,718
Restricted shares withheld for taxes	0	(55,510)	0	(1,218,326)	0	0	(1,273,836)
Restricted shares withheld for taxes (in shares)		(55,510)
Compensation expense for restricted shares	0	0	0	3,014,761	0	0	3,014,761
Compensation expense for stock options	0	0	0	12,470	0	0	12,470
Net income	0	0	0	0	42,405,607	0	42,405,607
Other comprehensive income	0	0	0	0	0	(13,579,028)	(13,579,028)
Ending Balances at Sep. 30, 2013	$ 0	$ 35,133,733	$ 0	$ 547,641,227	$ 129,792,296	$ (351,394)	$ 712,215,862
Balances (in shares) at Sep. 30, 2013		35,133,733