Income Taxes - Deferred tax assets (liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets:
Inventories	$ 455	$ 473
Accrued employees compensation and benefits costs	397	148
Postretirement obligation (accumulated other comprehensive income)	360	298
Accrued arbitration award and related liability		324
State Net operating loss and credit carryforwards	147	236
Bad debt reserve	40	71
Warranty reserve	80	88
Other	67
Total deferred tax assets	1,546	1,638
Valuation allowance	(147)	(236)
Net deferred tax asset	1,399	1,402
Deferred tax liabilities:
Prepaid expenses	(62)	(32)
Property, plant and equipment	(1,200)	(1,238)
Total deferred tax liabilities	(1,262)	(1,270)
Net deferred tax asset	$ 137	$ 132