SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Assets of VIE's (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 158,337	$ 375,580
Loans and leases	4,075,195	4,366,116
Allowance for credit losses	(45,336)	(49,705)	$ (45,947)	$ (68,281)
Accrued interest receivable	31,385	23,282
Other assets	260,070	292,327
Total assets	7,549,336	7,535,543	$ 6,747,410
Accrued expenses and other liabilities	424,292	248,863
Noncontrolling interest	(277)	(1,005)
Net assets less noncontrolling assets	839,882	$ 651,630
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	127
Loans and leases	51,835
Allowance for credit losses	(1,148)
Accrued interest receivable	163
Other assets	1,110
Total assets	52,087
Accrued expenses and other liabilities	338
Noncontrolling interest	(277)
Net assets less noncontrolling assets	$ 52,026