Note 11 - Business Segment and Geographic Financial Data (Tables)

3 Months Ended

Mar. 31, 2021

Notes Tables

Schedule of Segment Reporting Information, by Segment [Table Text Block]

	Air Pollution			FUEL CHEM
Three months ended March 31, 2021	Control Segment			Segment			Other			Total
Revenues from external customers	$	907		$	4,126		$	—		$	5,033
Cost of sales		(531	)		(2,144	)		—			(2,675	)
Gross margin		376			1,982			—			2,358
Selling, general and administrative		—			—			(3,100	)		(3,100	)
Research and development		—			—			(415	)		(415	)
Operating income (loss) from continuing operations	$	376		$	1,982		$	(3,515	)	$	(1,157	)

	Air Pollution			FUEL CHEM
Three months ended March 31, 2020	Control Segment			Segment			Other			Total
Revenues from external customers	$	1,196		$	2,582		$	—		$	3,778
Cost of sales		(765	)		(1,486	)		—			(2,251	)
Gross margin		431			1,096			—			1,527
Selling, general and administrative		—			—			(3,886	)		(3,886	)
Research and development		—			—			(324	)		(324	)
Operating income (loss) from continuing operations	$	431		$	1,096		$	(4,210	)	$	(2,683	)

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]

	Three Months Ended
	March 31,
	2021		2020
Revenues:
United States	$	4,463	$	3,097
Foreign		570		681
	$	5,033	$	3,778

	March 31,		December 31,
	2021		2020
Assets:
United States	$	45,379	$	24,524
Foreign		5,664		5,564
	$	51,043	$	30,088