Property, Plant and Equipment (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) a	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) a	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Property, Plant and Equipment
Property, plant and equipment - gross	$ 187,580,000		$ 187,580,000		$ 189,076,000
Less: accumulated depreciation and amortization, including accumulated amortization of capitalized leases	(98,113,000)		(98,113,000)		(92,980,000)
Total property, plant and equipment, net	89,467,000		89,467,000		96,096,000
Asset impairment charge			0
Proceeds from the sale of property, plant, and equipment			2,086,000	$ 143,000
Depreciation	2,938,000	$ 3,245,000	5,882,000	$ 6,527,000
Land
Property, Plant and Equipment
Property, plant and equipment - gross	$ 12,539,000		$ 12,539,000		14,869,000
Area of land (in acres) | a	54.5		54.5
Proceeds from the sale of property, plant, and equipment	$ 2,047,000
Loss on sale	269,000
Improvements to land and leaseholds
Property, Plant and Equipment
Property, plant and equipment - gross	17,482,000		$ 17,482,000		17,415,000
Buildings
Property, Plant and Equipment
Property, plant and equipment - gross	34,752,000		34,752,000		34,929,000
Machinery and equipment, including equipment under capitalized leases
Property, Plant and Equipment
Property, plant and equipment - gross	120,776,000		120,776,000		120,806,000
Construction in progress
Property, Plant and Equipment
Property, plant and equipment - gross	$ 2,031,000		$ 2,031,000		$ 1,057,000