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Note 1 - Summary of Significant Accounting Policies (Details Textual) $ in Millions		3 Months Ended	6 Months Ended
	Jan. 19, 2024 USD ($)	Dec. 31, 2023 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)
Number of Reportable Segments			3
Restricted Cash			$ 20.8	$ 14.3	$ 20.2
Payments to Acquire Businesses, Gross			$ 177.4	$ 37.1
MoGas Pipeline [Member]
Payments to Acquire Businesses, Gross	$ 177.6
Other Income [Member]
Gain on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring		$ 8.2