ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) security_loan	Dec. 31, 2021 USD ($) security_loan	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial allowance on acquired PCD loans	$ 26,103
Interest income on impaired loans	1,000	$ 800	$ 800
Loan workout and other credit costs	702	663	6,899
Troubled debt restructuring related reserves	600	$ 200
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial allowance on acquired PCD loans	$ 61
Number of loans in the process of foreclosure | security_loan	45	28
Total loans outstanding, residential loans	$ 6,700	$ 2,500
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans in the process of foreclosure | security_loan	8	9
Total loans outstanding, residential loans	$ 1,600	$ 3,200
Residential and Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan workout and other credit costs	$ 400	$ 1,500	$ 3,200
Impairment loans, charge off period	90 days
BMBC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial allowance on acquired PCD loans	$ 49,600
Loans purchased with no credit deterioration	23,500
Initial allowance on acquired PCD loans	$ 26,100