Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 8,231	$ 11,767
Supplies and service parts	21,841	21,475
Finished products	14,897	13,261
Inventory at FIFO cost, net	44,969	46,503
Excess of FIFO cost over LIFO cost	(3,005)	(5,734)
Total inventory, net	$ 41,964	$ 40,769