Business Segment and Geographic Financial Data - Reporting Segment Net Sales and Gross Margin (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Revenues from external customers	$ 12,791	$ 8,491
Cost of sales	(7,766)	(4,769)
Gross margin	5,025	3,722
Selling, general and administrative	(4,921)	(5,154)
Restructuring charge	0	(61)
Research and development	(288)	(284)
Operating loss from continuing operations	(184)	(1,777)
Air Pollution Control Segment
Revenues from external customers	8,583	4,002
Cost of sales	(5,597)	(2,500)
Gross margin	2,986	1,502
Selling, general and administrative	0	0
Restructuring charge		0
Research and development	0	0
Operating loss from continuing operations	2,986	1,502
FUEL CHEM Segment
Revenues from external customers	4,208	4,489
Cost of sales	(2,169)	(2,269)
Gross margin	2,039	2,220
Selling, general and administrative	0	0
Restructuring charge		(61)
Research and development	0	0
Operating loss from continuing operations	2,039	2,159
Other
Selling, general and administrative	(4,921)	(5,154)
Restructuring charge		0
Research and development	(288)	(284)
Operating loss from continuing operations	$ (5,209)	$ (5,438)

The aggregate cost of goods produced and sold and services rendered during the reporting period.

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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No definition available.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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The aggregate total costs related to selling a firm's product and services, as well as all other general and administrative expenses. Direct selling expenses (for example, credit, warranty, and advertising) are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc.

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