Reconciliation of Provision For Income Taxes Determined at Local Income Tax Rate to Effective Income Tax Rate (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of Effective Income Tax Rate [Line Items]
Pre-tax income	$ 78,672,847	$ 70,457,233	$ 52,965,551
United States federal corporate income tax rate	34.00%	34.00%	34.00%
Income tax computed at United States statutory corporate income tax rate	26,748,768	23,955,459	18,008,287
Loss not recognized as deferred tax assets	1,155,378	771,079	989,985
Non-deductible expenses	197,375	175,696	82,520
Change in fair value of warrants	17,241	(1,071,460)	429,053
Rate differential for PRC earnings	(7,399,559)	(6,260,780)	(5,126,705)
Other	11,641	(246,294)	116,436
Effective tax expense	$ 20,730,844	$ 17,323,700	$ 14,499,576