Business Segment and Geographic Financial Data - Reporting Segment Net Sales and Gross Margin (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues from external customers	$ 6,452	$ 16,070	$ 25,555	$ 40,708
Cost of sales	(3,563)	(10,654)	(14,754)	(26,545)
Gross margin	2,889	5,416	10,801	14,163
Selling, general and administrative	(3,822)	(4,105)	(12,735)	(13,789)
Restructuring charge	0	0	(625)	0
Research and development	(352)	(265)	(823)	(814)
Intangible assets abandonment	(76)	0	(127)	(317)
Operating income (loss) from continuing operations	(1,361)	1,046	(3,509)	(757)
Air Pollution Control Segment
Segment Reporting Information [Line Items]
Revenues from external customers	1,816	10,882	12,408	27,872
Cost of sales	(1,197)	(8,116)	(8,061)	(20,040)
Gross margin	619	2,766	4,347	7,832
Selling, general and administrative	0	0	0	0
Restructuring charge			0
Research and development	0	0	0	0
Intangible assets abandonment	0			0
Operating income (loss) from continuing operations	619	2,766	4,347	7,832
FUEL CHEM Segment
Segment Reporting Information [Line Items]
Revenues from external customers	4,636	5,188	13,147	12,836
Cost of sales	(2,366)	(2,538)	(6,693)	(6,505)
Gross margin	2,270	2,650	6,454	6,331
Selling, general and administrative	0	0	0	0
Restructuring charge			0
Research and development	0	0	0	0
Intangible assets abandonment	0			0
Operating income (loss) from continuing operations	2,270	2,650	6,454	6,331
Other
Segment Reporting Information [Line Items]
Revenues from external customers		0	0	0
Cost of sales	0	0	0	0
Gross margin	0	0	0	0
Selling, general and administrative	(3,822)	(4,105)	(12,735)	(13,789)
Restructuring charge			(625)
Research and development	(352)	(265)	(823)	(814)
Intangible assets abandonment	(76)		(127)	(317)
Operating income (loss) from continuing operations	$ (4,250)	$ (4,370)	$ (14,310)	$ (14,920)

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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