INVESTMENT SECURITIES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2024	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Debt securities pledged as collateral	$ 39,100		$ 45,100
Shareholder equity held by one issuer (as a percent)	10.00%	10.00%
Accrued interest receivable	$ 11,919		11,428
Bank Technology Fund
Debt Securities, Available-for-sale [Line Items]
Contractual obligation				$ 6,000
Payments to partnership fund	0
Balance with SBIC included in other assets	2,000
Committed investments to be made in the future	4,000
Debt securities pledged as collateral	9,600		39,300
Bank Technology Fund | Other Assets
Debt Securities, Available-for-sale [Line Items]
Contribution to committed investments			800
Small Business Investment Company ("SBIC")
Debt Securities, Available-for-sale [Line Items]
Contractual obligation	600
Return of capital, received	200		100
Small Business Investment Company ("SBIC") | Other Assets
Debt Securities, Available-for-sale [Line Items]
Contribution to committed investments	100		200
Balance with SBIC included in other assets	2,400		2,200
Held-to-Maturity Securities
Debt Securities, Available-for-sale [Line Items]
Accrued interest receivable	$ 500		$ 400