Accounts receivable, net (Schedule of Accounts Receivable) (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Accounts receivable, net [Abstract]
Accounts receivable	$ 27,581,588	$ 27,353,677
Less: allowance for doubtful debts	2,025,430	2,029,778
Accounts receivable, net	$ 25,556,158	$ 25,323,899