Reconciliation of Net Income and Weighted Average Shares Used in Computation of Basic and Diluted Earnings Per Share (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income available to common shareholders:
- Basic and diluted	$ 15,675,810	$ 13,446,666	$ 28,986,997	$ 24,921,678
Weighted average number of shares:
- Basic	29,825,336	29,820,836	29,823,098	29,810,996
- Effect of dilutive securities - warrants and options	168,244	197,149	149,516	238,340
- Diluted	29,993,580	30,017,985	29,972,614	30,049,336
Net income per share
- Basic	$ 0.53	$ 0.45	$ 0.97	$ 0.84
- Diluted	$ 0.52	$ 0.45	$ 0.97	$ 0.83