Leases - ROU Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Assets
Finance leases	$ 47,472	$ 50,118
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Public Utilities, Property, Plant and Equipment, Net	Public Utilities, Property, Plant and Equipment, Net
Operating leases	$ 223,366	$ 214,663
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Deferred charges and other assets	Deferred charges and other assets
Total right-of-use assets	$ 270,838	$ 264,781
Current
Finance leases	$ 1,568	$ 1,457
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Current maturities of long-term debt	Current maturities of long-term debt
Operating leases	$ 35,820	$ 38,644
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other current liabilities	Other current liabilities
Noncurrent
Finance leases	$ 48,825	$ 50,393
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt	Long-term debt
Operating leases	$ 194,452	$ 184,301
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Deferred credits and other liabilities	Deferred credits and other liabilities
Total	$ 280,665	$ 274,795