Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Raw materials	$ 17,879	$ 16,570
Supplies and service parts	25,749	24,061
Finished products	25,687	30,849
Inventory at FIFO cost	69,315	71,480
Excess of FIFO cost over LIFO cost	(5,635)	(5,635)
Total inventory, net	$ 63,680	$ 65,845