Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 38,322	$ 28,541
Work in process	10,541	6,498
Supplies and service parts	53,265	45,152
Finished products	31,493	24,678
Inventory at FIFO cost	133,621	104,869
Excess of FIFO cost over LIFO cost	(12,143)	(12,143)
Total inventory, net	$ 121,478	$ 92,726