Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Property, Plant and Equipment
Gross property, plant, and equipment	$ 166,710		$ 166,710		$ 159,304
Less accumulated depreciation and amortization, including accumulated amortization of finance leases	(103,989)		(103,989)		(98,869)
Property, plant, and equipment - net	62,721		62,721		60,435
Depreciation	1,940	$ 2,005	5,838	$ 5,985
Land
Property, Plant and Equipment
Gross property, plant, and equipment	6,599		6,599		6,612
Improvements to land and leaseholds
Property, Plant and Equipment
Gross property, plant, and equipment	17,548		17,548		17,172
Buildings
Property, Plant and Equipment
Gross property, plant, and equipment	25,766		25,766		25,370
Machinery and equipment, including equipment under finance leases
Property, Plant and Equipment
Gross property, plant, and equipment	108,867		108,867		106,372
Construction in progress
Property, Plant and Equipment
Gross property, plant, and equipment	$ 7,930		$ 7,930		$ 3,778