Provision for Income Tax (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
PRC income tax:
Current	$ 20,555,465	$ 17,388,836	$ 14,525,214
Deferred	175,379	(65,136)	(25,638)
Effective tax expense	$ 20,730,844	$ 17,323,700	$ 14,499,576