Summary of significant accounting policies (Schedule of Depreciation Rates of Plant and Equipment) (Details)	9 Months Ended
	Sep. 30, 2012
Buildings [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Depreciation rate	5.00%
Buildings [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Depreciation rate	10.00%
Furniture, Fixtures and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation rate	20.00%
Leasehold Improvement [Member]
Property, Plant and Equipment [Line Items]
Depreciation rate	50.00%
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation rate	10.00%
Motor Vehicles [Member]
Property, Plant and Equipment [Line Items]
Depreciation rate	20.00%