Commitments and contingencies (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies [Line Items]
Estimated Litigation Liability	$ 8,000,000
Litigation Settlement, Expense	100,000
Operating Leases, Rent Expense	2,700,000	$ 2,800,000	$ 3,000,000
Property, Plant and Equipment, Net, Total	5,397,000	$ 4,723,000
Liens Under Foreign Tax Authority [Member]
Commitments and Contingencies [Line Items]
Property, Plant and Equipment, Net, Total	$ 500,000