Intangible assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Identifiable intangible assets [Abstract]
Gross amount	$ 4,588	$ 4,284
Accumulated amortization	(3,771)	(3,487)
Amortization expense	284	128	$ 237
Future amortization expense [Abstract]
2020	237
2021	185
2022	154
2023	154
2024	87
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	0
Purchased Technology [Member]
Identifiable intangible assets [Abstract]
Gross amount	2,526	2,221
Accumulated amortization	(1,792)	(1,558)
Customer Relationships [Member]
Identifiable intangible assets [Abstract]
Gross amount	1,300	1,300
Accumulated amortization	(1,300)	(1,300)
Trademark [Member]
Identifiable intangible assets [Abstract]
Gross amount	480	480
Accumulated amortization	(402)	(354)
Covenant Not to Compete [Member]
Identifiable intangible assets [Abstract]
Gross amount	146	146
Accumulated amortization	(146)	(146)
Patents [Member]
Identifiable intangible assets [Abstract]
Gross amount	56	57
Accumulated amortization	(51)	(49)
Other [Member]
Identifiable intangible assets [Abstract]
Gross amount	80	80
Accumulated amortization	$ (80)	$ (80)