Inventories (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Inventories
Finished goods	$ 11,809	$ 8,323
Work-in-process	4,241	5,393
Raw materials and purchased parts	25,735	21,188
Stores and supplies	39,590	35,589
Total inventories	81,375	70,493
Valued at lower of cost or market:
LIFO basis	15,473	14,133
FIFO basis	8,826	7,567
Average cost basis	57,076	48,793
Total inventories	81,375	70,493
Excess of inventories valued at current costs over LIFO	14,000	14,000
Change in income as a result of LIFO basis inventory valuation over FIFO basis valuation	$ 0	$ 0