Note 3 - Revenue 1 (Details Textual) Pure in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Contract with Customer, Liability, Current	$ 1,683		$ 1,683		$ 721	$ 1,279
Contract with Customer, Liability, Revenue Recognized	$ 171	$ 438	$ 543	$ 1,221
Contract with Customer, Contracts in Progress, Number of Contracts Identified as Loss Contracts	0		0		0
Revenue, Remaining Performance Obligation, Amount	$ 7,811		$ 7,811
Air Pollution Control [Member]
Contract with Customer, Asset, after Allowance for Credit Loss	$ 1,064		$ 1,064		$ 2,075	$ 2,285