Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials	$ 16,631	$ 13,514
Supplies and service parts	24,133	21,840
Finished products	35,156	36,969
Inventory at FIFO cost	75,920	72,323
Excess of FIFO cost over LIFO cost	(4,072)	(4,072)
Total inventory, net	$ 71,848	$ 68,251