Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Raw materials	$ 19,289	$ 16,570
Supplies and service parts	26,162	24,061
Finished products	29,680	30,849
Inventory at FIFO cost	75,131	71,480
Excess of FIFO cost over LIFO cost	(5,635)	(5,635)
Total inventory, net	$ 69,496	$ 65,845