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Note 5 - Other Investments (Details Textual) - RGC Midstream LLC [Member] - USD ($)
$ in Millions
3 Months Ended
Sep. 30, 2022
Mar. 31, 2022
Sep. 30, 2023
MVP Southgate Investment [Member]      
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners     1.00%
MVP [Member]      
Equity Method Investment, Ownership Percentage     1.00%
Long Term Investment, Other than Temporary Impairment $ 15.3 $ 39.8