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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Organization and Significant Accounting Policies (Detail)	3 Months Ended	12 Months Ended
	Dec. 31, 2014 USD ($) shares	Dec. 31, 2015 USD ($) customer unit shares	Dec. 31, 2014 USD ($) customer shares	Dec. 31, 2013 USD ($) customer shares	Dec. 31, 2012 shares
Revenues from external customers		$ 73,664,000	$ 79,017,000	$ 109,338,000
Percentage of foreign net income		30.00%	36.00%	42.00%
Unbilled contracts receivable	$ 6,910,000	$ 5,454,000	$ 6,910,000
Bankers acceptance	2,259,000	$ 2,144,000	2,259,000
Number of reporting units \| unit		2
Impairment of Intangible Assets, Finite-lived		$ 1,425,000	0	$ 0
Intangible assets impairment		0	23,400,000
Patents	$ 1,583,000	1,699,000	1,583,000
Identifiable intangible assets		5,158,000
Purchases of other intangible assets		$ 0	3,010,000	0
Useful Life (Years)		5 years
Amortization of intangible assets		$ 2,138,000	2,384,000	839,000
Depreciation		$ 2,067,000	$ 1,922,000	$ 2,175,000
Options outstanding (in shares) \| shares	1,546,500	1,191,125	1,546,500	1,688,500	1,914,000
Antidilutive equity awards (In shares) \| shares		169,000	280,000
Available-for-sale securities	$ 36,000	$ 19,000	$ 36,000
Treasury shares withheld (in shares) \| shares		84,486	58,649
Treasury shares withheld		$ 252,000	$ 304,000	$ 447,000
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	$ 376,000	$ 244,000	$ 376,000
Minimum
Warranty period (in years)		1 year
Maximum
Warranty period (in years)		2 years
Antidilutive
Options outstanding (in shares) \| shares	1,628,000	2,068,000	1,628,000	1,623,000
FUEL CHEM Segment
Revenues from external customers		$ 30,179,000	$ 36,986,000	$ 36,786,000
Impairment of Intangible Assets, Finite-lived		0
Intangible assets impairment		$ 0	0
FUEL CHEM Segment \| Sales Revenue, Services, Net
Concentration risk percentage		12.00%
APC Technology Segment
Intangible assets impairment	$ 23,400,000	$ 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	$ 9,904,000	7,312,000	$ 9,904,000
Foreign
Revenues from external customers		$ 22,179,000	$ 28,116,000	$ 46,063,000
Reserved For Issuance Upon Exercise Or Vesting Of Equity Awards
Number of shares reserved for future issuance \| shares		4,400,676
Chinese Subsidiary
Restricted cash and cash equivalents		$ 5,596,000
Italian Subsidiary
Cash		1,286,000
Carbonette Fuel Conversion Process
Purchases of other intangible assets		$ 3,010,000