Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 30,166	$ 28,541
Work in process	4,981	6,498
Supplies and service parts	45,366	45,152
Finished products	21,765	24,678
Inventory at FIFO cost, net	102,278	104,869
Excess of FIFO cost over LIFO cost	(12,599)	(12,143)
Total inventory, net	$ 89,679	$ 92,726