STOCK-BASED COMPENSATION - STOCK-BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense included in operation and maintenance expense	$ 14,716	$ 14,827	$ 7,149
Income tax benefit	(3,563)	(3,624)	(1,613)
Total, net of tax	11,153	11,203	5,536
Taxes related to stock-based compensation	(588)	(144)	(159)
Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense included in operation and maintenance expense	4,882	4,131	3,856
Restricted and non-restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense included in operation and maintenance expense	3,647	3,189	3,193
Deferred retention stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense included in operation and maintenance expense	$ 6,187	$ 7,507	$ 100