Income taxes - Deferred income tax assets (liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred income tax assets (liabilities)
- Reserves for doubtful accounts	$ 497	$ 500
- Inventory reserve	687	1,045
- Non qualified stock options	529	383
- Deferred interest		2,637
- Accrued expenses	82	107
Net deferred income tax assets	1,795	4,672
- Depreciation & amortization	(6,353)	(4,916)
Total deferred tax assets	(6,353)	(4,916)
Net deferred income tax liabilities	$ (4,558)	$ (244)