Business Segment, Geographic and Quarterly Financial Data - Reporting Segment Net Sales and Gross Margin (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from external customers	$ 9,568,000	$ 12,596,000	$ 15,175,000	$ 17,822,000	$ 18,201,000	$ 21,677,000	$ 18,683,000	$ 15,103,000	$ 55,161,000	$ 73,664,000	$ 79,017,000
Cost of sales	$ (7,717,000)	$ (7,281,000)	$ (9,595,000)	$ (11,774,000)	$ (11,294,000)	$ (13,829,000)	$ (11,547,000)	$ (8,437,000)	(36,367,000)	(45,107,000)	(43,889,000)
Gross margin									18,794,000	28,557,000	35,128,000
Selling, general and administrative									(25,564,000)	(30,897,000)	(35,432,000)
Restructuring charge									(1,428,000)	(219,000)	0
Research and development									(4,552,000)	(4,273,000)	(1,459,000)
Goodwill and intangible assets impairment									(2,074,000)	(1,425,000)	(23,400,000)
Operating (loss)									(14,824,000)	(8,257,000)	(25,163,000)
Air Pollution Control Segment
Revenues from external customers									34,052,000	43,485,000	42,031,000
Cost of sales									(25,370,000)	(30,612,000)	(26,586,000)
Gross margin									8,682,000	12,873,000	15,445,000
Selling, general and administrative									0	0	0
Restructuring charge									(537,000)	(149,000)	0
Research and development									0	0	0
Goodwill and intangible assets impairment									0	(1,425,000)	(23,400,000)
Operating (loss)									8,145,000	11,299,000	(7,955,000)
FUEL CHEM Segment
Revenues from external customers									21,109,000	30,179,000	36,986,000
Cost of sales									(10,997,000)	(14,495,000)	(17,303,000)
Gross margin									10,112,000	15,684,000	19,683,000
Selling, general and administrative									0	0	0
Restructuring charge									(891,000)	(70,000)	0
Research and development									0	0	0
Goodwill and intangible assets impairment									0	0	0
Operating (loss)									9,221,000	15,614,000	19,683,000
Fuel Conversion Segment
Revenues from external customers									0	0	0
Cost of sales									0	0	0
Gross margin									0	0	0
Selling, general and administrative									0	0	0
Restructuring charge									0	0	0
Research and development									(2,800,000)	(2,826,000)	(277,000)
Goodwill and intangible assets impairment									0	0	0
Operating (loss)									(2,800,000)	(2,826,000)	(277,000)
Other
Revenues from external customers									0	0	0
Cost of sales									0	0	0
Gross margin									0	0	0
Selling, general and administrative									(25,564,000)	(30,897,000)	(35,432,000)
Restructuring charge									0	0	0
Research and development									(1,752,000)	(1,447,000)	(1,182,000)
Goodwill and intangible assets impairment									(2,074,000)	0	0
Operating (loss)									$ (29,390,000)	$ (32,344,000)	$ (36,614,000)