Change in accounting principle, Effect of Change on Statements of Operations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Condensed Consolidated Statements of Operations [Abstract]
Cost of sales	$ 7,189	$ 7,136	$ 5,893	$ 14,325	$ 10,855
Gross profit	5,434	2,566	3,432	8,000	6,771
Operating loss	(2,954)	(5,604)	(2,648)	(8,558)	(5,164)
Loss before income taxes	(3,246)	(5,703)	(2,694)	(8,949)	(5,306)
Income tax benefit	870	1,355	664	2,225	1,187
Net loss	$ (2,376)	$ (4,348)	$ (2,030)	$ (6,724)	$ (4,119)
Net loss per common share [Abstract]
Basic (in dollars per share)	$ (0.24)	$ (0.44)	$ (0.23)	$ (0.68)	$ (0.46)
Diluted (in dollars per share)	$ (0.24)	$ (0.44)	$ (0.23)	$ (0.68)	$ (0.46)
Shares used in per-share calculation [Abstract]
Basic (in shares)	9,910	9,886	8,976	9,898	8,962
Diluted (in shares)	9,910	9,886	8,976	9,898	8,962
Previously Reported [Member]
Condensed Consolidated Statements of Operations [Abstract]
Cost of sales		$ 6,708	$ 6,000		$ 11,112
Gross profit		2,994	3,325		6,514
Operating loss		(5,176)	(2,755)		(5,421)
Loss before income taxes		(5,275)	(2,801)		(5,563)
Income tax benefit		1,262	687		1,243
Net loss		$ (4,013)	$ (2,114)		$ (4,320)
Net loss per common share [Abstract]
Basic (in dollars per share)		$ (0.41)	$ (0.24)		$ (0.48)
Diluted (in dollars per share)		$ (0.41)	$ (0.24)		$ (0.48)
Shares used in per-share calculation [Abstract]
Basic (in shares)		9,886	8,976		8,962
Diluted (in shares)		9,886	8,976		8,962
Effect of Change [Member] | Change in Method of Inventory Valuation to Average Costing [Member]
Condensed Consolidated Statements of Operations [Abstract]
Cost of sales		$ 428	$ (107)		$ (257)
Gross profit		(428)	107		257
Operating loss		(428)	107		257
Loss before income taxes		(428)	107		257
Income tax benefit		93	(23)		(56)
Net loss		$ (335)	$ 84		$ 201
Net loss per common share [Abstract]
Basic (in dollars per share)		$ (0.03)	$ 0.01		$ 0.02
Diluted (in dollars per share)		$ (0.03)	$ 0.01		$ 0.02