Segment reporting and concentrations (Details 2) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 15,674	$ 16,060	$ 15,642	$ 15,698	$ 15,523	$ 15,135	$ 14,063	$ 13,802	$ 63,074	$ 58,523	$ 59,076
Other - principally Europe
Segment Reporting Information [Line Items]
Revenues									7,555	5,607	5,478
United States [Member]
Segment Reporting Information [Line Items]
Revenues									32,070	28,412	31,489
The Netherlands
Segment Reporting Information [Line Items]
Revenues									9,216	9,610	9,870
United Kingdom
Segment Reporting Information [Line Items]
Revenues									8,271	9,070	9,113
Canada
Segment Reporting Information [Line Items]
Revenues									$ 5,962	$ 5,824	$ 3,126