Investments in Privately-Held Raw Material Companies - Minority Investment Entities (Details) - Five Minority Investments - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Summarized income information of all the minority investment entities that are not consolidated and accounted for under the equity method [Abstract]
Net revenue	$ 3,605,000	$ 4,559,000	$ 7,558,000	$ 11,000,000
Gross profit (loss)	958,000	1,165,000	2,026,000	1,114,000
Operating (loss)	265,000	618,000	462,000	(1,421,000)
Net income (loss)	(160,000)	430,000	(158,000)	(2,016,000)
Minority investment entities
Entity portion of loss from unconsolidated equity method investments, including impairment charges	$ 168,000	$ 8,000	$ 300,000	$ 1,600,000