Property, Plant and Equipment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Property, Plant and Equipment
Gross property, plant, and equipment	$ 191,785,000		$ 191,785,000		$ 188,655,000
Less accumulated depreciation and amortization, including accumulated amortization of finance leases	(107,344,000)		(107,344,000)		(101,798,000)
Property, plant, and equipment - net	84,441,000		84,441,000		86,857,000
Depreciation	2,768,000	$ 2,938,000	5,540,000	$ 5,882,000
Asset impairment			0	$ 0
Land
Property, Plant and Equipment
Gross property, plant, and equipment	12,443,000		12,443,000		12,440,000
Improvements to land and leaseholds
Property, Plant and Equipment
Gross property, plant, and equipment	17,580,000		17,580,000		17,610,000
Buildings
Property, Plant and Equipment
Gross property, plant, and equipment	36,474,000		36,474,000		34,608,000
Machinery and equipment, including equipment under finance leases
Property, Plant and Equipment
Gross property, plant, and equipment	122,596,000		122,596,000		120,914,000
Construction in progress
Property, Plant and Equipment
Gross property, plant, and equipment	$ 2,692,000		$ 2,692,000		$ 3,083,000