Income Taxes - Narrative (Details) - USD ($)	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Taxes [Line Items]
Taxes refundable to customers	$ 306,335,000	$ 305,645,000
Recoverable future taxes	89,247,000	80,084,000
Unrecognized tax benefits	0	0	$ 0
Deferred Income Taxes
Income Taxes [Line Items]
Taxes refundable to customers	306,300,000	305,600,000
Recoverable future taxes	$ 89,200,000	$ 80,100,000