LEASES - RIGHT-OF-USE ASSETS AND LEASE LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Noncurrent
Operating lease assets	$ 185,596	$ 184,485
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Utility plant, at cost	Utility plant, at cost
Finance lease assets	$ 24,402	$ 26,088
Total lease assets	209,998	210,573
Current
Operating lease liabilities	$ 4,388	$ 4,945
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Current maturities of long-term debt	Current maturities of long-term debt
Finance lease liabilities	$ 5,568	$ 7,534
Noncurrent
Operating lease liabilities	$ 159,131	$ 159,303
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt	Long-term debt
Finance lease liabilities	$ 10,366	$ 16,026
Total lease liabilities	$ 179,453	$ 187,808