Property and equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total	$ 27,291	$ 25,795
Less: accumulated depreciation and amortization	(21,894)	(21,072)
Property, Plant and Equipment, Net	5,397	4,723
Equipment [Member]
Property, Plant and Equipment [Line Items]
Total	14,558	13,437
Software [Member]
Property, Plant and Equipment [Line Items]
Total	5,685	5,089
Furniture and equipment [Member]
Property, Plant and Equipment [Line Items]
Total	2,119	2,313
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Total	$ 4,929	$ 4,956