Property, Plant and Equipment, net (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment, net
Original cost of fully depreciated assets still in use	$ 147,900,000	$ 131,300,000
Depreciation expense	20,100,000	19,000,000	16,300,000
Property, Plant and Equipment
Property, plant and equipment, gross	438,782,000	425,224,000
Less accumulated depreciation and amortization	(235,535,000)	(217,868,000)
Property, plant and equipment excluding capital projects in progress, net	203,247,000	207,356,000
Capital projects in progress	6,286,000	6,096,000
Property, plant and equipment, net	209,533,000	213,452,000
Land
Property, Plant and Equipment
Property, plant and equipment, gross	29,347,000	32,068,000
Buildings and site improvements
Property, Plant and Equipment
Property, plant and equipment, gross	178,391,000	174,187,000
Leasehold improvements
Property, Plant and Equipment
Property, plant and equipment, gross	5,213,000	4,747,000
Machinery and equipment
Property, Plant and Equipment
Property, plant and equipment, gross	$ 225,831,000	$ 214,222,000