Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 39,287	$ 28,541
Work in process	6,620	6,498
Supplies and service parts	51,854	45,152
Finished products	32,664	24,678
Inventory at FIFO cost	130,425	104,869
Excess of FIFO cost over LIFO cost	(12,143)	(12,143)
Total inventory, net	$ 118,282	$ 92,726