Summary of significant accounting policies (Property, Plant and Equipment Estimated Useful Lives) (Details)	12 Months Ended
Dec. 31, 2014
Servers, computers and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Furniture, fixtures and office equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Motor vehicles [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration