FAIR VALUE - Assets and liabilities measured on a non-recurring basis (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2023	Mar. 31, 2024
Assets and Liabilities Measured on Nonrecurring Basis
Valuation allowance		$ 470	$ 965
FBD
Assets and Liabilities Measured on Nonrecurring Basis
Estimated probability of achievement		100.00%
TGA
Assets and Liabilities Measured on Nonrecurring Basis
Acquisition-related contingent consideration adjustment		$ 1,000
Payment of contingent consideration	$ 2,400
Maximum | FBD
Assets and Liabilities Measured on Nonrecurring Basis
Acquisition-related contingent consideration adjustment		2,700
Mortgage servicing rights
Assets and Liabilities Measured on Nonrecurring Basis
Valuation allowance			1,200
Non-recurring
Assets and Liabilities Measured on Nonrecurring Basis
Individually assessed loans		3,014	9,224
Other real estate owned		1,159	1,742
Mortgage servicing rights		162	76
Contingent consideration		(5,150)	(8,216)
Total		(815)	2,826
Non-recurring | Level 1
Assets and Liabilities Measured on Nonrecurring Basis
Individually assessed loans		0	0
Other real estate owned		0	0
Mortgage servicing rights		0	0
Contingent consideration		0	0
Total		0	0
Non-recurring | Level 2
Assets and Liabilities Measured on Nonrecurring Basis
Individually assessed loans		0	0
Other real estate owned		0	0
Mortgage servicing rights		0	0
Contingent consideration		0	0
Total		0	0
Non-recurring | Level 3
Assets and Liabilities Measured on Nonrecurring Basis
Individually assessed loans		3,014	9,224
Other real estate owned		1,159	1,742
Mortgage servicing rights		162	76
Contingent consideration		(5,150)	(8,216)
Total		$ (815)	$ 2,826