Note 9 - Information by Operating Segment - Total Assets by Segment (Details) - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Total Assets	$ 10,327.7	$ 10,083.7	$ 9,650.5
Operating Segments [Member] | Gas Utility [Member]
Total Assets	8,355.1	8,042.8	7,882.1
Operating Segments [Member] | Gas Marketing [Member]
Total Assets	492.4	638.7	424.4
Operating Segments [Member] | Midstream [Member]
Total Assets	466.6	446.0	421.7
Operating Segments [Member] | Other Segments [Member]
Total Assets	2,882.8	2,449.2	1,995.9
Consolidation, Eliminations [Member]
Total Assets	$ (1,869.2)	$ (1,493.0)	$ (1,073.6)