Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 835,341	$ 762,187
Less accumulated depreciation	(476,043)	(427,698)
Property, plant and equipment, net	359,298	334,489
Depreciation expense	48,693	43,165	$ 39,654
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	21,723	19,952
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	182,226	169,695
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 631,392	$ 572,540