EMPLOYEE BENEFIT PLANS - Schedule of net periodic costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Amortization of:
Total net periodic (benefits) costs	$ (907)	$ (1,559)	$ (3,148)
Supplemental Employee Retirement Plan
Net periodic (benefits) costs:
Interest cost	162	335	503
Expected return on plan assets	0	0	0
Amortization of:
Prior service costs	0	14	14
Actuarial loss	516	399	258
Total net periodic (benefits) costs	678	748	775
Pension Plan
Net periodic (benefits) costs:
Interest cost	2,816	4,267	5,778
Expected return on plan assets	(10,177)	(10,343)	(10,331)
Amortization of:
Prior service costs	0	0	0
Actuarial loss	5,776	3,769	630
Total net periodic (benefits) costs	$ (1,585)	$ (2,307)	$ (3,923)