Line of credit (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Line of Credit Facility [Line Items]
Line of credit	$ 53,853,092	$ 56,478,396
Unused line of credit	19,878,138	33,890,616
Debt covenant, percentage of total net assets	20.00%
Bank of China [Member]
Line of Credit Facility [Line Items]
Starting date	Jan. 13, 2012
Maturity date	Jan. 12, 2013
Line of credit	7,954,437
Unused line of credit	241,815
Wing Lung Bank Ltd. [Member]
Line of Credit Facility [Line Items]
Starting date	Mar. 29, 2012	Aug. 29, 2011
Maturity date	Mar. 28, 2013	Mar. 20, 2012
Line of credit	2,600,000	2,600,000
Unused line of credit
Wing Lung Bank Ltd. [Member]
Line of Credit Facility [Line Items]
Starting date	Apr. 20, 2012	Aug. 29, 2011
Maturity date	Apr. 19, 2013	Mar. 20, 2012
Line of credit	2,708,244	2,574,665
Unused line of credit
The Shanghai Commercial & Saving bank [Member]
Line of Credit Facility [Line Items]
Starting date	Aug. 08, 2012
Maturity date	Jun. 07, 2013
Line of credit	4,000,000
Unused line of credit
Industrial and Commercial Bank of China [Member]
Line of Credit Facility [Line Items]
Starting date	Jul. 26, 2012	Nov. 29, 2011
Maturity date	Jul. 25, 2013	Aug. 31, 2013
Line of credit	6,363,550	6,343,568
Unused line of credit	2,395,876	4,898,820
Shenzhen Development Bank Co., Ltd [Member]
Line of Credit Facility [Line Items]
Starting date	Dec. 12, 2011	Dec. 12, 2011
Maturity date	Nov. 27, 2012	Nov. 27, 2012
Line of credit	15,908,874	15,858,919
Unused line of credit	4,672,436	10,768,206
China Everbright Bank [Member]
Line of Credit Facility [Line Items]
Starting date	Aug. 01, 2012	Jun. 09, 2011
Maturity date	Jul. 31, 2013	Jun. 09, 2012
Line of credit	7,954,437	7,929,460
Unused line of credit	6,999,905	3,103,590
China Resources Bank Of Zhuhai [Member]
Line of Credit Facility [Line Items]
Starting date	Apr. 28, 2012
Maturity date	Apr. 28, 2013
Line of credit	6,363,550
Unused line of credit	5,568,106
Standard Chartered (China) Co., Ltd. [Member]
Line of Credit Facility [Line Items]
Starting date		Jan. 21, 2011
Maturity date		Mar. 30, 2012
Line of credit		2,000,000
Unused line of credit		2,000,000
Standard Chartered (Hong Kong) Co., Ltd. [Member]
Line of Credit Facility [Line Items]
Starting date		Jan. 21, 2011
Maturity date		Jan. 21, 2012
Line of credit		13,000,000
Unused line of credit		10,120,000
Citibank (Hong Kong) Co., Ltd. [Member]
Line of Credit Facility [Line Items]
Starting date		Jan. 31, 2011
Maturity date		Jan. 31, 2012
Line of credit		3,000,000
Unused line of credit		$ 3,000,000