LEASES - RIGHT-OF-USE ASSETS AND LEASE LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Noncurrent
Operating lease assets	$ 175,864	$ 175,740
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Utility plant, at cost	Utility plant, at cost
Finance lease assets	$ 27,720	$ 28,248
Total lease assets	203,584	203,988
Current
Operating lease liabilities	$ 4,798	$ 4,772
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	$ 9,433	$ 8,477
Noncurrent
Operating lease liabilities	$ 148,849	$ 148,023
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt	Long-term debt
Finance lease liabilities	$ 19,964	$ 22,875
Total lease liabilities	$ 183,044	$ 184,147