Organization and Significant Accounting Policies (Detail)	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) shares	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) shares	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) customer unit shares	Dec. 31, 2015 USD ($) customer shares	Dec. 31, 2014 USD ($) customer shares	Dec. 31, 2013 shares
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
Percentage of foreign net income									23.00%	30.00%	36.00%
Restricted cash	6,020,000				0				$ 6,020,000	$ 0
Unbilled contracts receivable	5,025,000				5,454,000				5,025,000	5,454,000
Bankers acceptance	838,000				2,144,000				838,000	2,144,000
Excess and obsolete inventory reserve	825,000				0				$ 825,000	0
Number of reporting units | unit									2
Goodwill and intangible assets impairment									$ 2,074,000	1,425,000	$ 23,400,000
Intangible assets impairment									0	0	23,400,000
Patents	1,656,000				$ 1,699,000				1,656,000	1,699,000
Identifiable intangible assets	$ 5,158,000								5,158,000
Purchases of other intangible assets									$ 0	0	3,010,000
Useful Life (Years)									5 years
Amortization of intangible assets									$ 1,720,000	2,138,000	2,384,000
Depreciation									$ 1,780,000	$ 2,067,000	$ 1,922,000
Options outstanding (in shares) | shares	1,039,750				1,191,125				1,039,750	1,191,125	1,546,500	1,688,500
Antidilutive equity awards (In shares) | shares									184,000	169,000
Available-for-sale securities	$ 9,000				$ 19,000				$ 9,000	$ 19,000
Treasury shares withheld (in shares) | shares									103,097	84,486
Treasury shares withheld									$ 172,000	$ 252,000	$ 304,000
Sales Revenue, Services, Net
Number of customers | customer									1	2	2
Concentration risk percentage									10.00%	10.00%	10.00%
Accounts Receivable
Number of customers | customer									0	0	0
Concentration risk percentage									10.00%	10.00%	10.00%
Capitalized Third-party Costs
Patents	$ 166,000				$ 244,000				$ 166,000	$ 244,000
Minimum
Warranty period (in years)									1 year
Maximum
Warranty period (in years)									2 years
Antidilutive
Options outstanding (in shares) | shares	1,800,000				2,068,000				1,800,000	2,068,000	1,628,000
FUEL CHEM Segment
Revenues from external customers									$ 21,109,000	$ 30,179,000	$ 36,986,000
Goodwill and intangible assets impairment									0	0	0
Intangible assets impairment									$ 0	0	0
FUEL CHEM Segment | Sales Revenue, Services, Net
Concentration risk percentage									19.00%
APC Technology Segment
Intangible assets impairment					$ 23,400,000				$ 0	$ 0	$ 23,400,000
Customer One | FUEL CHEM Segment | Sales Revenue, Services, Net
Number of customers										1	1
Concentration risk percentage										20.00%	14.00%
Customer One | APC Technology Segment | Sales Revenue, Services, Net
Concentration risk percentage										11.00%	18.00%
Project and Non-Project
Unbilled contracts receivable	$ 6,755,000				$ 7,312,000				6,755,000	$ 7,312,000
Foreign
Revenues from external customers									$ 12,616,000	$ 22,179,000	$ 28,116,000
Reserved For Issuance Upon Exercise Or Vesting Of Equity Awards
Number of shares reserved for future issuance | shares	4,400,676								4,400,676
Incentive Plan
Number of shares reserved for future issuance | shares	748,742								748,742
Inventories
Excess and obsolete inventory reserve	$ 175,000								$ 175,000
Other Assets
Excess and obsolete inventory reserve	650								650
Chinese Subsidiary
Restricted cash and cash equivalents	3,222,000								3,222,000
Italian Subsidiary
Cash	$ 2,408,000								2,408,000
Carbonette Fuel Conversion Process
Purchases of other intangible assets									$ 3,010,000