Property, Plant and Equipment, Net (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Property, Plant and Equipment
Property, plant and equipment, gross	$ 442,699	$ 438,782	$ 422,860
Less accumulated depreciation and amortization	(240,289)	(235,535)	(221,468)
Property, plant and equipment excluding capital projects in progress, net	202,410	203,247	201,392
Capital projects in progress	5,047	6,286	9,618
Property, plant and equipment, net	207,457	209,533	211,010
Land
Property, Plant and Equipment
Property, plant and equipment, gross	29,960	29,347	30,364
Buildings and site improvements
Property, Plant and Equipment
Property, plant and equipment, gross	178,135	178,391	173,923
Leasehold improvements
Property, Plant and Equipment
Property, plant and equipment, gross	5,492	5,213	4,708
Machinery, equipment, and software
Property, Plant and Equipment
Property, plant and equipment, gross	$ 229,112	$ 225,831	$ 213,865