Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Net income, basic	$ 8,482,239	$ 16,940,194	$ 23,626,643
Effect of Interest related to Convertible Debt	0	0	2,942,004
Net income available to common stockholders, diluted	$ 8,482,239	$ 16,940,194	$ 26,568,647
Denominator:
Denominator for basic earnings per share-weighted-average shares	13,225,448	13,242,702	13,194,226
Effect of dilutive securities:
Common stock options and restricted stock awards	129,165	78,907	91,550
Convertible Debt	0	0	1,678,740
Denominator for diluted earnings per share-adjusted weighted-average shares assumed conversion	13,354,613	13,321,609	14,964,516
Basic earnings per share	$ 0.64	$ 1.28	$ 1.79
Diluted earnings per share	$ 0.64	$ 1.27	$ 1.78