Business and summary of significant accounting policies - Property and equipment (Details)	12 Months Ended
	Dec. 31, 2016
Computer and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	5 years
Computer and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	7 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	5 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life of property and equipment	7 years