Accrued product warranty liability (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Accrued product warranty liability [Roll Forward]
Balance, beginning of period	$ 140	$ 215
Warranties issued	39	53
Warranty settlements	(70)	(107)
Balance, end of period	109	$ 161
Accrued product warranty liability, current	88
Other Liabilities [Member]
Accrued product warranty liability [Roll Forward]
Accrued product warranty liability, non-current	$ 21
Maximum [Member]
Warranty [Abstract]
Product warranty period	24 months