Property, Plant and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, plant and equipment
Property, plant and equipment, gross	$ 183,779,000	$ 174,584,000
Accumulated depreciation	(109,123,000)	(103,549,000)
Property, plant and equipment, net	74,656,000	71,035,000
Depreciation expense	7,400,000	6,000,000	6,100,000
Land, buildings and improvements
Property, plant and equipment
Property, plant and equipment, gross	85,849,000	83,032,000
Machinery, equipment and fixtures
Property, plant and equipment
Property, plant and equipment, gross	79,597,000	73,169,000
Office furniture, equipment and vehicles
Property, plant and equipment
Property, plant and equipment, gross	18,116,000	18,058,000
Construction in progress
Property, plant and equipment
Property, plant and equipment, gross	$ 217,000	$ 325,000