LEASES - RIGHT-OF-USE ASSETS AND LEASE LIABILITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
NONCURRENT ASSETS
Operating lease assets	$ 171,207	$ 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	$ 22,828	$ 13,489
Total lease assets	194,035	187,417
Current
Operating lease liabilities	$ 4,878	$ 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	$ 6,443	$ 5,393
Noncurrent
Operating lease liabilities	$ 140,036	$ 141,363
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt	Long-term debt
Finance lease liabilities	$ 27,045	$ 14,742
Total lease liabilities	$ 178,402	$ 165,798