Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Rental expense	$ 6,507	$ 6,043	$ 5,464
Capital Lease Obligations Incurred	762
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	323,305	307,710
Less: Accumulated depreciation	(207,076)	(185,681)
Total property, plant and equipment	116,229	122,029
Operating Leases
2018	6,832
2019	6,117
2020	3,448
2021	2,239
2022	2,099
Thereafter	3,613
Capital Leases
2018	246
2019	246
2020	116
2021	0
2022	0
Thereafter	0
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,027	4,027
Building and improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	91,766	90,780
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	219,675	205,674
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 7,837	$ 7,229