Inventories (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Inventories
Finished goods	$ 15,565	$ 11,809
Work-in-process	1,114	2,030
Raw materials and purchased parts	23,542	27,946
Stores and supplies	46,071	39,590
Total inventories	86,292	81,375
Valued at lower of cost or market:
LIFO basis	10,532	15,473
FIFO basis	9,265	8,826
Average cost basis	66,495	57,076
Total inventories	86,292	81,375
Excess of inventories valued at current costs over LIFO	13,000	14,000
Change in income as a result of LIFO basis inventory valuation over FIFO basis valuation	$ 1,200	$ 0	$ 0