Business Segment and Geographic Financial Data - Reporting Segment Net Sales and Gross Margin (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues from external customers	$ 16,070,000	$ 13,548,000	$ 40,708,000	$ 31,780,000
Cost of sales	(10,654,000)	(8,498,000)	(26,545,000)	(19,383,000)
Gross margin	5,416,000	5,050,000	14,163,000	12,397,000
Selling, general and administrative	(4,105,000)	(4,968,000)	(13,789,000)	(16,045,000)
Restructuring charge	0	0	0	(119,000)
Research and development	(265,000)	(216,000)	(814,000)	(780,000)
Intangible assets abandonment			(317,000)
Building impairment				(2,965,000)
Operating income (loss) from continuing operations	1,046,000	(134,000)	(757,000)	(7,512,000)
Air Pollution Control Segment
Segment Reporting Information [Line Items]
Revenues from external customers	10,882,000	8,799,000	27,872,000	18,346,000
Cost of sales	(8,116,000)	(6,184,000)	(20,040,000)	(12,787,000)
Gross margin	2,766,000	2,615,000	7,832,000	5,559,000
Selling, general and administrative	0	0	0	0
Restructuring charge				(58,000)
Research and development	0	0	0	0
Operating income (loss) from continuing operations	2,766,000	2,615,000	7,832,000	5,501,000
FUEL CHEM Segment
Segment Reporting Information [Line Items]
Revenues from external customers	5,188,000	4,749,000	12,836,000	13,434,000
Cost of sales	(2,538,000)	(2,314,000)	(6,505,000)	(6,596,000)
Gross margin	2,650,000	2,435,000	6,331,000	6,838,000
Selling, general and administrative	0	0	0	0
Restructuring charge				(61,000)
Research and development	0	0	0	0
Operating income (loss) from continuing operations	2,650,000	2,435,000	6,331,000	6,777,000
Other
Segment Reporting Information [Line Items]
Selling, general and administrative	(4,105,000)	(4,968,000)	(13,789,000)	(16,045,000)
Restructuring charge				0
Research and development	(265,000)	(216,000)	(814,000)	(780,000)
Intangible assets abandonment			(317,000)
Building impairment				(2,965,000)
Operating income (loss) from continuing operations	$ (4,370,000)	$ (5,184,000)	$ (14,920,000)	$ (19,790,000)

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