CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) (USD $)	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comp. Income (Loss), Net [Member]	Total
Balances at Dec. 31, 2012	$ 34,696,597	$ 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 and related tax benefits	88,845	902,533	0	0	991,378
Exercise of employee common stock options and related tax benefits (in shares)	88,845
Common dividends paid					0
Issuance of restricted common shares, net of forfeitures	274,545	(274,545)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)	274,545
Restricted shares withheld for taxes	(37,500)	(731,679)	0	0	(769,179)
Restricted shares withheld for taxes (in shares)	(37,500)
Compensation expense for restricted shares	0	950,498	0	0	950,498
Compensation expense for stock options	0	12,471	0	0	12,471
Net income	0	0	13,448,125	0	13,448,125
Other comprehensive income (loss)	0	0	0	(2,270,910)	(2,270,910)
Ending Balances at Mar. 31, 2013	35,022,487	544,619,717	100,834,814	10,956,724	691,433,742
Balances (in shares) at Mar. 31, 2013	35,022,487
Balances at Dec. 31, 2013	35,221,941	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 and related tax benefits	136,482	1,981,567	0	0	2,118,049
Exercise of employee common stock options and related tax benefits (in shares)	136,482
Common dividends paid	0	0	(2,824,493)	0	(2,824,493)
Issuance of restricted common shares, net of forfeitures	260,937	(260,937)	0	0	0
Issuance of restricted common shares, net of forfeitures (in shares)	260,937
Restricted shares withheld for taxes	(52,092)	(1,672,312)	0	0	(1,724,404)
Restricted shares withheld for taxes (in shares)	(52,092)
Compensation expense for restricted shares	0	1,201,111	0	0	1,201,111
Net income	0	0	16,367,123	0	16,367,123
Other comprehensive income (loss)	0	0	0	3,651,606	3,651,606
Ending Balances at Mar. 31, 2014	$ 35,567,268	$ 551,461,564	$ 155,840,829	$ (373,008)	$ 742,496,653
Balances (in shares) at Mar. 31, 2014	35,567,268