Business Segment and Geographic Financial Data - Reporting Segment Net Sales and Gross Margin (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues from external customers	$ 8,948	$ 11,847	$ 19,103	$ 24,638
Cost of sales	(5,050)	(8,125)	(11,191)	(15,891)
Gross margin	3,898	3,722	7,912	8,747
Selling, general and administrative	(4,455)	(4,763)	(8,913)	(9,684)
Restructuring charge	(30)	0	(625)	0
Research and development	(205)	(261)	(471)	(549)
Asset Impairment Charges	(51)	(317)	(51)	(317)
Operating loss from continuing operations	(843)	(1,619)	(2,148)	(1,803)
Air Pollution Control Segment
Segment Reporting Information [Line Items]
Revenues from external customers	4,803	8,407	10,592	16,990
Cost of sales	(2,975)	(6,328)	(6,864)	(11,924)
Gross margin	1,828	2,079	3,728	5,066
Selling, general and administrative	0	0	0	0
Restructuring charge	(30)		(625)
Research and development	0	0	0	0
Asset Impairment Charges		0		0
Operating loss from continuing operations	1,798	2,079	3,103	5,066
FUEL CHEM Segment
Segment Reporting Information [Line Items]
Revenues from external customers	4,145	3,440	8,511	7,648
Cost of sales	(2,075)	(1,797)	(4,327)	(3,967)
Gross margin	2,070	1,643	4,184	3,681
Selling, general and administrative	0	0	0	0
Restructuring charge	0		0
Research and development	0	0	0	0
Asset Impairment Charges		0		0
Operating loss from continuing operations	2,070	1,643	4,184	3,681
Other
Segment Reporting Information [Line Items]
Selling, general and administrative	(4,455)	(4,763)	(8,913)	(9,684)
Restructuring charge	0		0
Research and development	(205)	(261)	(471)	(549)
Asset Impairment Charges	(51)	(317)	(51)	(317)
Operating loss from continuing operations	$ (4,711)	$ (5,341)	$ (9,435)	$ (10,550)

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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