Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment
Property, plant and equipment, gross	$ 718,875	$ 643,863
Less accumulated depreciation	(352,433)	(332,844)
Property, plant and equipment, net	366,442	311,019	$ 290,586
Depreciation expense	36,300	33,700	$ 28,200
Accrued pension and other liabilities
Property, Plant and Equipment
Asset retirement obligations	1,800
Land and improvements
Property, Plant and Equipment
Property, plant and equipment, gross	37,479	32,522
Mineral rights
Property, Plant and Equipment
Property, plant and equipment, gross	11,240
Buildings
Property, Plant and Equipment
Property, plant and equipment, gross	90,385	67,841
Machinery, equipment and customer capital
Property, Plant and Equipment
Property, plant and equipment, gross	494,722	458,975
Computer hardware and software
Property, Plant and Equipment
Property, plant and equipment, gross	43,631	41,850
Furniture and vehicles
Property, Plant and Equipment
Property, plant and equipment, gross	10,893	10,534
Construction-in-progress
Property, Plant and Equipment
Property, plant and equipment, gross	$ 30,525	$ 32,141