Property, Plant and Equipment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment
Gross property, plant, and equipment	$ 171,390,000		$ 171,390,000		$ 168,638,000
Less accumulated depreciation and amortization, including accumulated amortization of finance leases	(110,864,000)		(110,864,000)		(106,553,000)
Property, plant, and equipment - net	60,526,000		60,526,000		62,085,000
Depreciation	2,018,000	$ 1,963,000	4,008,000	$ 3,898,000
Impairments of property, plant, and equipment			0	$ 0
Land
Property, Plant and Equipment
Gross property, plant, and equipment	6,636,000		6,636,000		6,627,000
Improvements to land and leaseholds
Property, Plant and Equipment
Gross property, plant, and equipment	17,771,000		17,771,000		17,573,000
Buildings
Property, Plant and Equipment
Gross property, plant, and equipment	27,598,000		27,598,000		27,348,000
Machinery and equipment, including equipment under finance leases
Property, Plant and Equipment
Gross property, plant, and equipment	118,060,000		118,060,000		116,175,000
Construction in progress
Property, Plant and Equipment
Gross property, plant, and equipment	$ 1,325,000		$ 1,325,000		$ 915,000