Reconciliation of Basic and Diluted Net Income Per Share (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	$ 10,994,695	$ 8,366,617	$ 20,353,591	$ 25,261,540
Weighted average number of common shares outstanding - Basic	64,334,400	53,578,218	63,073,008	53,286,072
Effect of dilutive securities:
Unexercised warrants and options	152,538	668,345	237,026	914,480
Weighted average number of common shares outstanding - Diluted	64,486,938	54,246,563	63,310,034	54,200,552
Earnings per share-Basic	$ 0.17	$ 0.16	$ 0.32	$ 0.47
Earnings per share-Diluted	$ 0.17	$ 0.15	$ 0.32	$ 0.47