Short-term loans (Details) (USD $)			6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Short-term Debt [Member]
Short-term Debt [Line Items]
Short- term bank loans guaranteed and repayable within one year	$ 27,636,005	$ 20,478,604
Land use right pledged as collateral			3,092,149
Property, plant and equipment pledged as collateral	10,422,899
Receivables pledged as collateral for bank loans	$ 10,497,137
Minimum interest rate			1.30%
Maximum interest rate			6.90%