Note 10 - Derivative Instruments and Hedging Activities (Tables)

12 Months Ended

Sep. 30, 2023

Notes Tables

Schedule of Derivative Instruments [Table Text Block]

	September 30, 2023		September 30, 2022
Gas Marketing	Notional (MMBtu millions)	Maximum Term (Months)	Notional (MMBtu millions)	Maximum Term (Months)
Natural gas futures purchased	61.3	51	76.3	54
Natural gas options purchased, net	4.9	15	3.7	12
Natural gas basis swaps purchased	44.1	51	61.7	39
Gas Utility
Natural gas futures purchased	66.5	24	13.0	12

	September 30, 2023				September 30, 2022
	Notional (MMBtu millions)		Maximum Term (Months)		Notional (MMBtu millions)		Maximum Term (Months)
Natural gas futures purchased		66.5		24		13.0		12

Derivative Instruments, Gain (Loss) [Table Text Block]

Effect of Derivative Instruments on the Consolidated Statements of Income and Comprehensive Income
	Location of Gain (Loss)
	Recorded in Income	2023			2022			2021
Derivatives in Cash Flow Hedging Relationships
Effective portion of gain recognized in OCI on derivatives:
Interest rate swaps		$	20.1		$	56.7		$	61.2
Effective portion of gain reclassified from AOCI to income:
Interest rate swaps	Interest Expense	$	(2.4	)	$	(1.2	)	$	(1.3	)
Derivatives Not Designated as Hedging Instruments*
Gain (Loss) recognized in income on derivatives:
Gas / diesel futures	Non-Operating Expense: Other Income	$	0.3		$	—		$	—
Natural gas commodity contracts	Operating Expenses: Natural Gas		18.0			52.6			54.1
NYMEX / ICE natural gas contracts	Operating Expenses: Natural Gas		(35.0	)		43.3			(77.5	)
Total		$	(16.7	)	$	95.9		$	(23.4	)

Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]

Fair Value of Derivative Instruments in the Consolidated Balance Sheets
	Derivative Assets*			Derivative Liabilities*
September 30, 2023	Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value
Derivatives designated as hedging instruments
Other: Interest rate swaps	Current Assets: Other	$	44.2	Current Liabilities: Other	$	—
Subtotal			44.2			—
Derivatives not designated as hedging instruments
Gas Utility:
Natural gas contracts	Current Assets: Other		6.3	Current Liabilities: Other		50.8
Gasoline and heating oil contracts	Current Assets: Other		0.1			—
Gas Marketing:
NYMEX / ICE natural gas contracts	Current Assets: Other		8.0	Current Liabilities: Other		16.0
	Deferred Charges and Other Assets: Other		2.1	Deferred Credits and Other Liabilities: Other		5.7
Natural gas commodity	Current Assets: Other		31.2	Current Liabilities: Other		20.1
	Deferred Charges and Other Assets: Other		5.5	Deferred Credits and Other Liabilities: Other		7.6
Subtotal			53.2			100.2
Total derivatives		$	97.4		$	100.2
September 30, 2022
Derivatives designated as hedging instruments
Other: Interest rate swaps	Current Assets: Other	$	63.6	Current Liabilities: Other	$	—
Subtotal			63.6			—
Derivatives not designated as hedging instruments
Gas Utility:
Natural gas contracts	Current Assets: Other		57.8	Current Liabilities: Other		30.7
Gas Marketing:
NYMEX / ICE natural gas contracts	Current Assets: Other	79.2		Current Liabilities: Other		71.5
	Deferred Charges and Other Assets: Other		12.7	Deferred Credits and Other Liabilities: Other		10.8
Natural gas commodity	Current Assets: Other		53.4	Current Liabilities: Other		55.1
	Deferred Charges and Other Assets: Other		3.1	Deferred Credits and Other Liabilities: Other		10.4
Subtotal			206.2			178.5
Total derivatives		$	269.8		$	178.5

Fair Value of Derivative Instruments in the Balance Sheets
	Derivative Assets*			Derivative Liabilities*
September 30, 2023	Balance Sheet Location	Fair Value		Balance Sheet Location	Fair Value
Derivatives not designated as hedging instruments
Natural gas contracts	Current Assets: Other	$	6.3	Current Liabilities: Other	$	50.8
Gasoline and heating oil contracts	Current Assets: Other		0.1
Total derivatives		$	6.4		$	50.8
September 30, 2022
Derivatives not designated as hedging instruments
Natural gas contracts	Current Assets: Other	$	57.8	Current Liabilities: Other	$	30.7

Derivative Instrument Reconciliation [Table Text Block]

	2023			2022
Fair value of derivative assets presented above	$	97.4		$	269.8
Fair value of cash margin receivable offset with derivatives		49.3			(36.6	)
Netting of assets and liabilities with the same counterparty		(69.4	)		(117.0	)
Total	$	77.3		$	116.2
Derivative Instrument Assets, per Consolidated Balance Sheets:
Current Assets: Other	$	71.8		$	113.1
Deferred Charges and Other Assets: Other		5.5			3.1
Total	$	77.3		$	116.2
Fair value of derivative liabilities presented above	$	100.2		$	178.5
Netting of assets and liabilities with the same counterparty		(69.4	)		(117.0	)
Total	$	30.8		$	61.5
Derivative Instrument Liabilities, per Consolidated Balance Sheets:
Current Liabilities: Other	$	23.2		$	51.1
Deferred Credits and Other Liabilities: Other		7.6			10.4
Total	$	30.8		$	61.5

	2023			2022
Fair value of derivative assets presented above	$	6.4		$	57.8
Fair value of cash margin (payable) receivable offset with derivatives		37.6			(27.1	)
Netting of assets and liabilities with the same counterparty		(44.0	)		(30.7	)
Total	$	—		$	—
Fair value of derivative liabilities presented above	$	50.8		$	30.7
Netting of assets and liabilities with the same counterparty		(44.0	)		(30.7	)
Total	$	6.8		$	—
Derivative Instrument Liabilities, per Balance Sheets:
Derivative instrument liabilities	$	6.8		$	—
Total	$	6.8		$	—

Interest Rate Swap [Member]

Notes Tables

Schedule of Derivative Instruments [Table Text Block]

Period Originated	Contract Hedge Term (Years)		Notional Amount		Fixed Interest Rate			Fiscal 2023 Mark-to-Market Gain
Quarter 1, fiscal 2022		10	$	50.0		1.4918	%	$	2.7
Quarter 2, fiscal 2022		10		75.0		1.6475	%		4.0
Quarter 2, fiscal 2022		10		25.0		1.7460	%		1.5
Quarter 1, fiscal 2023		10		50.0		3.4480	%		2.4
Quarter 2, fiscal 2023		10		50.0		3.6850	%		0.9
Quarter 2, fiscal 2023		10		25.0		3.5350	%		0.5
Quarter 2, fiscal 2023		10		25.0		3.3850	%		0.6
Quarter 3, fiscal 2023		30		50.0		2.7470	%		7.8
Quarter 3, fiscal 2023		10		25.0		2.9020	%		2.2
Quarter 3, fiscal 2023		10		25.0		3.0180	%		2.0
			$	400.0				$	24.6