Business Segment, Geographic and Quarterly Financial Data - Reporting Segment Net Sales and Gross Margin (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues from external customers	$ 4,912,000	$ 6,452,000	$ 8,948,000	$ 10,155,000	$ 15,827,000	$ 16,070,000	$ 11,847,000	$ 12,791,000	$ 30,467,000	$ 56,535,000	$ 45,166,000
Cost of sales	$ (4,883,000)	$ (3,563,000)	$ (5,050,000)	$ (6,141,000)	$ (9,926,000)	$ (10,654,000)	$ (8,125,000)	$ (7,766,000)	(19,637,000)	(36,471,000)	(27,144,000)
Gross margin									10,830,000	20,064,000	18,022,000
Selling, general and administrative									(17,191,000)	(18,564,000)	(20,933,000)
Restructuring charges									(625,000)	0	(119,000)
Intangible assets abandonment									(1,127,000)	(1,073,000)	(1,070,000)
Operating income (loss) from continuing operations									(127,000)	(317,000)	(2,965,000)
Operating income (loss) from continuing operations									(8,240,000)	110,000	(7,065,000)
Air Pollution Control Segment
Revenues from external customers									14,082,000	38,417,000	27,808,000
Cost of sales									(11,256,000)	(27,382,000)	(18,478,000)
Gross margin									2,826,000	11,035,000	9,330,000
Selling, general and administrative									0	0	0
Restructuring charges									(625,000)		(58,000)
Intangible assets abandonment									0	0	0
Operating income (loss) from continuing operations									0	0	0
Operating income (loss) from continuing operations									2,201,000	11,035,000	9,272,000
FUEL CHEM Segment
Revenues from external customers									16,385,000	18,118,000	17,358,000
Cost of sales									(8,381,000)	(9,089,000)	(8,666,000)
Gross margin									8,004,000	9,029,000	8,692,000
Selling, general and administrative									0	0	0
Restructuring charges									0		(61,000)
Intangible assets abandonment									0	0	0
Operating income (loss) from continuing operations									0	0	0
Operating income (loss) from continuing operations									8,004,000	9,029,000	8,631,000
Other
Revenues from external customers									0	0	0
Cost of sales									0	0	0
Gross margin									0	0	0
Selling, general and administrative									(17,191,000)	(18,564,000)	(20,933,000)
Restructuring charges									0		0
Intangible assets abandonment									(1,127,000)	(1,073,000)	(1,070,000)
Operating income (loss) from continuing operations									(127,000)	(317,000)	(2,965,000)
Operating income (loss) from continuing operations									$ (18,445,000)	$ (19,954,000)	$ (24,968,000)