Note 2 - Principles of Consolidation and Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounts Receivable, Allowance for Credit Loss	$ 0	$ 60
Unrecognized Tax Benefits		0	$ 0
Impairment of Long-Lived Assets to be Disposed of	$ 0	$ 0
Building and Building Improvements [Member]
Property, Plant and Equipment, Useful Life (Year)	25 years
Tangible Asset Impairment Charges	$ 0
Pipelines [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)	10 years
Pipelines [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)	22 years