Income taxes, Components of income tax provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current [Abstract]
Federal	$ 58	$ 1,049	$ 2,379
State	51	85	114
Foreign	36	13	(49)
Income taxes current	145	1,147	2,444
Deferred [Abstract]
Federal	(205)	(117)	1,097
State	5	10	20
Foreign	(94)	0	0
Income taxes deferred	(294)	(107)	1,117
Income tax provision (benefit)	$ (149)	$ 1,040	$ 3,561
Income taxes [Abstract]
U.S. corporate income tax rate	21.00%	21.00%	34.00%
Undistributed foreign E&P			$ 0
Income tax expense related to undistributed foreign subsidiary E&P			0
Provisional income tax expense			1,300
Income taxes [Abstract]
Foreign loss before taxes	$ 515	$ 286	$ 563
Federal [Member]
Income taxes [Abstract]
Net operating loss carryforward	0
State [Member]
Income taxes [Abstract]
Net operating loss carryforward	0
Tax credit carryforward	0
R&D Credit [Member]
Income taxes [Abstract]
Tax credit carryforward	$ 111
Maximum [Member]
Income taxes [Abstract]
U.S. corporate income tax rate			35.00%