LEASES - RIGHT-OF-USE ASSETS AND LEASE LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Sep. 30, 2025
Noncurrent Assets
Operating lease assets	$ 188,889	$ 185,596
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Utility plant, at cost	Utility plant, at cost
Finance lease assets	$ 24,020	$ 24,402
Total lease assets	212,909	209,998
Current Liabilities
Operating lease liabilities	$ 4,694	$ 4,388
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	$ 4,861	$ 5,568
Noncurrent Liabilities
Operating lease liabilities	$ 162,984	$ 159,131
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt	Long-term debt
Finance lease liabilities	$ 9,110	$ 10,366
Total lease liabilities	$ 181,649	$ 179,453