LEASES - RIGHT-OF-USE ASSETS AND LEASE LIABILITIES (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
NONCURRENT ASSETS
Operating lease assets	$ 169,884	$ 173,928
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Utility plant, at cost	Utility plant, at cost
Finance lease assets	$ 22,370	$ 13,489
Total lease assets	192,254	187,417
Current
Operating lease liabilities	$ 4,893	$ 4,300
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	$ 6,491	$ 5,393
Noncurrent
Operating lease liabilities	$ 139,289	$ 141,363
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt	Long-term debt
Finance lease liabilities	$ 25,404	$ 14,742
Total lease liabilities	$ 176,077	$ 165,798