Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Investment Plan, Maximum Amount. Approved			$ 20,000
Inventory, Net	$ 537	$ 439
Equipment Constructed for Resale [Member]
Inventory, Net	207	207
Spare Parts [Member]
Inventory, Net	330	232
In Process Equipment [Member]
Inventory, Net	$ 607	$ 618
Minimum [Member]
Debt Securities, Held-to-maturity, Maturity Term (Month)	3 months
Maximum [Member]
Debt Securities, Held-to-maturity, Maturity Term (Month)	36 months
Asset Pledged as Collateral [Member] | Letter of Credit [Member]
Restricted Cash and Investments	$ 1,332
Asset Pledged as Collateral [Member] | Letter of Credit [Member] | Varying Maturity Dates Expiring No Later Than September 30, 2024 [Member]
Restricted Cash and Investments	1,134
Asset Pledged as Collateral [Member] | Letter of Credit [Member] | Latest Maturity Date No Later Than November 30, 2025 [Member]
Restricted Cash and Investments	$ 198