Reconciliation of Provision For Income Taxes Determined at Local Income Tax Rate to Effective Income Tax Rate (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reconciliation of Effective Income Tax Rate [Line Items]
Pre-tax income	$ 21,233,295	$ 18,296,275	$ 39,259,170	$ 34,048,633
United States federal corporate income tax rate	34.00%	34.00%	34.00%	34.00%
Income tax computed at United States statutory corporate income tax rate	7,219,320	6,220,733	13,348,118	11,576,535
Loss not recognized as deferred tax assets	230,090	257,658	483,807	600,187
Non-deductible expenses	69,809	81,674	66,381	74,444
Change in fair value of warrants and gain on extinguishment of warrants	(26,017)	14,960	10,703	136,241
Rate differential for PRC earnings	(1,964,905)	(1,724,138)	(3,665,928)	(3,267,003)
Other	29,188	(1,278)	29,092	6,551
Effective tax expense	$ 5,557,485	$ 4,849,609	$ 10,272,173	$ 9,126,955