Note 9 - Fair Value Measurements - Schedule of Derivative Assets and Liabilities, Including Receivables and Payables (Details) (Parentheticals) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Assets [Abstract]
Regulatory Asset, Current	$ 115.4	$ 348.3
Liabilities [Abstract]
Regulatory Liability, Current	$ 49.5	$ 7.3
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Regulatory Asset, Current	Regulatory Asset, Current
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Regulatory Liability, Current	Regulatory Liability, Current

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Indicates line item in statement of financial position that includes derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

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Indicates line item in statement of financial position that includes derivative liability.

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No definition available.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 340
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
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The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 405
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477571/980-405-25-1

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