Property, Plant and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Land and land improvements	$ 18,374,000	$ 17,201,000
Buildings and structures	36,174,000	33,985,000
Machinery and equipment	176,085,000	171,385,000
Construction in progress	5,878,000	1,225,000
Property, Plant and Equipment, Gross	236,511,000	223,796,000
Less: accumulated depreciation	(170,762,000)	(163,820,000)
Property, Plant and Equipment, Net	65,749,000	59,976,000
Depreciation	$ 8,100,000	$ 8,200,000	$ 8,800,000