Note 3 - Revenue 1 (Details Textual) Pure in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2025 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Contract with Customer, Liability, Current	$ 627		$ 721	$ 1,279
Contract with Customer, Liability, Revenue Recognized	$ 372	$ 1,121
Contract with Customer, Contracts in Progress, Number of Contracts Identified as Loss Contracts	0		0
Revenue, Remaining Performance Obligation, Amount	$ 10,328
Air Pollution Control [Member]
Contract with Customer, Asset, after Allowance for Credit Loss	$ 572		$ 2,075	$ 2,285