LOANS AND ALLOWANCE FOR CREDIT LOSSES - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable Allowance For Credit Losses [Line Items]
Accrued interest receivable	$ 37,900,000			$ 37,400,000
Less: allowance for credit losses on loans	96,285,000	$ 96,188,000		91,684,000	$ 93,180,000
Provision (reversal) for credit losses on loans	5,315,000	3,200,000
Non accrual loans interest income	$ 0		$ 0
Concessions granted, percent to loan portfolio (less than)	1.00%
Commitments to lend additional amounts	$ 1,400,000
Unfunded Loan Commitment
Financing Receivable Allowance For Credit Losses [Line Items]
Less: allowance for credit losses on loans	10,100,000			$ 11,300,000
Provision (reversal) for credit losses on loans	$ (1,200,000)	$ 466,000