Note 1 - Organization and Significant Accounting Policies (Details Textual) $ in Thousands		12 Months Ended
	Oct. 03, 2025 USD ($)	Dec. 31, 2025 USD ($) shares	Dec. 31, 2024 USD ($) shares	Dec. 31, 2023 shares
Cash		$ 9,318	$ 7,879
Investment Plan, Maximum Amount. Approved		20,000
Unbilled Contracts Receivable		887	2,075
Inventory, Net		373	397
Inventory Valuation Reserves		$ 613	613
Number of Reporting Units		2
Goodwill		$ 2,116	2,116
Goodwill, Impairment Loss		0	0
Payments to Acquire Productive Assets		674	378
Finite-Lived Intangible Assets, Gross		1,207	852
Amortization of Intangible Assets		36	57
Depreciation		663	403
Impairment, Long-Lived Asset, Held-for-Use		0	0
Defined Contribution Plan, Cost		$ 264	$ 249
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares) | shares		71,000	176,000	270,500
Class of Warrant or Right, Outstanding (in shares) | shares		2,850,000	2,850,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) | shares		260,600	274,900
Treasury Stock, Shares, Acquired (in shares) | shares		147,685	83,050
Treasury Stock, Value, Acquired, Cost Method		$ 222	$ 95
Employee Retention Credit Receivable		$ 0	$ 1,677
Customer Concentration Risk [Member] | Revenue Benchmark [Member]
Number of Major Customers		3	2
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Three Customers [Member]
Concentration Risk, Percentage		43.00%
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Two Customers [Member]
Concentration Risk, Percentage			27.00%
Antidilutive [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares) | shares		66,600	168,900
Class of Warrant or Right, Outstanding (in shares) | shares		2,850,000	2,850,000
The 2014 Long-term Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares) | shares		0
Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares) | shares		2,668,885
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares) | shares		2,883,057
Patents [Member]
Finite-Lived Intangible Assets, Gross		$ 867	$ 852
Other Intangible Assets [Member]
Finite-Lived Intangible Assets, Gross		$ 340	0
Finite-Lived Intangible Asset, Useful Life (Year)		10 years
Wahlco [Member] | Technology Rights, Patents, and Trademarks [Member]
Payments to Acquire Productive Assets	$ 350
Wahlco [Member] | Patents [Member]
Finite-Lived Intangible Assets, Gross	10
Wahlco [Member] | Other Intangible Assets [Member]
Finite-Lived Intangible Assets, Gross	$ 340
Wahlco [Member] | Intellectual Property [Member]
Finite-Lived Intangible Asset, Useful Life (Year)	10 years
Capitalized Third-party Costs [Member]
Finite-Lived Patents, Gross		$ 5	26
FUEL CHEM Technology Segment [Member]
Goodwill		$ 2,116	$ 2,116
FUEL CHEM Technology Segment [Member] | Customer Concentration Risk [Member] | Revenue Benchmark [Member]
Number of Major Customers		3	2
Equipment Constructed for Resale [Member]
Inventory, Net		$ 176	$ 176
Spare Parts [Member]
Inventory, Net		197	221
In Process Equipment [Member]
Inventory, Net		$ 53	44
Minimum [Member]
Debt Securities, Held-to-maturity, Maturity Term (Month)		3 months
Standard Product Warranty Period (Year)		1 year
Minimum [Member] | Patents [Member]
Finite-Lived Intangible Asset, Useful Life (Year)		1 year
Minimum [Member] | APC Technology [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)		8 years
Maximum [Member]
Debt Securities, Held-to-maturity, Maturity Term (Month)		36 months
Standard Product Warranty Period (Year)		2 years
Maximum [Member] | Patents [Member]
Finite-Lived Intangible Asset, Useful Life (Year)		20 years
Maximum [Member] | APC Technology [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)		20 years
Asset Pledged as Collateral [Member] | Letter of Credit [Member]
Restricted Cash and Investments		$ 3,655
Asset Pledged as Collateral [Member] | Letter of Credit [Member] | Varying Maturity Dates Expiring No Later Than October 8, 2028 [Member]
Restricted Cash and Investments		2,437
Non-US [Member]
Revenues		$ 5,655	$ 7,331
Percentage of Revenue		21.00%	29.00%
CHINA
Cash		$ 515
ITALY
Cash		411
CHILE
Cash		$ 147