Property, Plant and Equipment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment - gross	$ 189,440,000		$ 189,440,000		$ 185,495,000
Less accumulated depreciation and amortization, including accumulated amortization of capitalized leases	87,887,000		87,887,000		81,522,000
Total property, plant and equipment, net	101,553,000		101,553,000		103,973,000
Asset impairment charge			0
Depreciation	3,245,000	$ 3,598,000	6,527,000	$ 7,325,000
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment - gross	14,851,000		14,851,000		14,826,000
Improvements to land and leaseholds
Property, Plant and Equipment [Line Items]
Property, plant and equipment - gross	17,404,000		17,404,000		17,408,000
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment - gross	34,209,000		34,209,000		33,910,000
Machinery and equipment, including equipment under capitalized leases
Property, Plant and Equipment [Line Items]
Property, plant and equipment - gross	121,975,000		121,975,000		118,060,000
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment - gross	$ 1,001,000		$ 1,001,000		$ 1,291,000