Note 12 - Business Segment, Geographic and Quarterly Financial Data (Detail) - Reporting Segment Net Sales and Gross Margin (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues from external customers	$ 97,644	$ 93,668	$ 81,795
Cost of sales	(56,899)	(49,857)	(46,821)
Gross margin	40,745	43,811	34,974
Selling, general and administrative	(32,682)	(33,446)	(30,857)
Gain from revaluation of ACT liability		758	768
Research and development	(2,863)	(1,474)	(948)
Operating income	5,200	9,649	3,937
Air Pollution Control Segment [Member]
Revenues from external customers	62,441	50,930	40,917
Cost of sales	(40,146)	(28,467)	(27,024)
Gross margin	22,295	22,463	13,893
Selling, general and administrative	0	0	0
Gain from revaluation of ACT liability		0	0
Research and development	0	0	0
Operating income	22,295	22,463	13,893
Fuel Chem Segment [Member]
Revenues from external customers	35,203	42,738	40,878
Cost of sales	(16,753)	(21,390)	(19,797)
Gross margin	18,450	21,348	21,081
Selling, general and administrative	0	0	0
Gain from revaluation of ACT liability		0	0
Research and development	0	0	0
Operating income	18,450	21,348	21,081
Other Segments [Member]
Revenues from external customers	0	0	0
Cost of sales	0	0	0
Gross margin	0	0	0
Selling, general and administrative	(32,682)	(33,446)	(30,857)
Gain from revaluation of ACT liability		758	768
Research and development	(2,863)	(1,474)	(948)
Operating income	$ (35,545)	$ (34,162)	$ (31,037)