Segment information (Schedule of Geographic Information about Accounts Receivable) (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Accounts receivable	$ 25,556,158	$ 25,323,899
Hong Kong and China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Accounts receivable	16,768,440	15,575,555
Asia, Others [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Accounts receivable	2,071,529	2,435,129
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Accounts receivable	6,170,287	5,537,976
North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Accounts receivable	469,090	1,632,644
South America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Accounts receivable	49,724	97,097
Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Accounts receivable	27,088	35,164
Others [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Accounts receivable		$ 10,334