SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Assets of VIE's (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 388,038	$ 314,019
Loans and leases	3,536,305	3,609,563
Allowance for credit losses	(45,947)	(68,281)	$ (56,188)
Accrued interest receivable	17,979	16,254
Other assets	295,324	212,276
Total assets	6,747,410	6,690,650	$ 6,092,074
Accrued expenses and other liabilities	200,205	210,961
Noncontrolling interest	(30)	1,155
Net assets less noncontrolling assets	645,170	$ 870,729
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	604
Loans and leases	81,881
Allowance for credit losses	(3,720)
Accrued interest receivable	345
Foreclosed real estate and repossessed assets, net	1
Other assets	1,727
Total assets	80,838
Accrued expenses and other liabilities	1,280
Noncontrolling interest	(30)
Net assets less noncontrolling assets	$ 79,588