LOANS AND ALLOWANCE FOR CREDIT LOSSES ON LOANS (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from the sale of mortgage loans	$ 41,913	$ 35,501
Gain on sale of mortgage loans	(470)	(384)
Loans held for sale, at fair value (book value of $9,441 and $10,152, respectively)	9,524		$ 10,320
Allowance for Loan and Lease Losses, Period Increase (Decrease)	1,300
Allowance for credit losses	35,613	37,134	36,935	$ 36,922
(Credit) provision for loan losses	$ (1,164)	439	1,174
Other industry exposures	0
Non-Accrual Loans	$ 5,658		5,448
Loans outstanding	4,121,040		4,098,094
Interest lost on nonaccrual loans	43	25
Loans and Leases Receivable, Excluded Accrued Interest from Amortized Cost	13,000		12,700
FHLB advances, general debt obligations, pledged collateral	1,900,000
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,762,482		1,763,378
Proceeds from the sale of mortgage loans	41,400	35,100
Gain on sale of mortgage loans	(470)	(384)
Loans held for sale, at fair value (book value of $9,441 and $10,152, respectively)	9,400		10,200
Unrealized gain (loss) on loans held for sale	83		168
Allowance for Loan and Lease Losses, Period Increase (Decrease)	(85)	85
Allowance for credit losses	10,565	10,812	10,254	9,089
(Credit) provision for loan losses	305	1,737	1,139
Non-Accrual Loans	2,473		2,541
Loans outstanding	1,762,482		1,763,378
Mortgage Loans in Process of Foreclosure, Amount	952		1,100
Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,402,326		1,370,446
Allowance for credit losses	15,294	16,324	16,581	17,296
(Credit) provision for loan losses	(1,294)	(973)	(734)
Non-Accrual Loans	82		261
Loans outstanding	1,402,326		1,370,446
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Loan and Lease Losses, Period Increase (Decrease)	1,300
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	397,395		403,901
Allowance for credit losses	4,460	4,581	4,869	5,446
(Credit) provision for loan losses	(192)	(652)	512
Non-Accrual Loans	1,980		1,725
Loans outstanding	397,395		403,901
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	240,674		240,341
Allowance for credit losses	2,360	2,440	2,217	2,225
(Credit) provision for loan losses	63	215	(9)
Non-Accrual Loans	994		759
Loans outstanding	240,674		240,341
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	17,537		18,168
Allowance for credit losses	704	507	724	$ 504
(Credit) provision for loan losses	14	$ 4	280
Non-Accrual Loans	6		37
Loans outstanding	17,537		18,168
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	397,395		403,901
Financing Receivable, Year One, Originated, Current Fiscal Year	6,841		42,164
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	39,972		54,911
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	$ 52,815		56,550
Non-Residential Building Operators Industry Sector \| Loan Concentration Risk \| Total Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percentage)	13.00%
Non-Residential Building Operators Industry Sector \| Loan Concentration Risk \| Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percentage)	32.00%
Residential Building Operators Industry Sector \| Loan Concentration Risk \| Total Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percentage)	11.00%
Residential Building Operators Industry Sector \| Loan Concentration Risk \| Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percentage)	28.00%
Substandard [Member] \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 8,377		9,033
Financing Receivable, Year One, Originated, Current Fiscal Year	0		248
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	234		588
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	484		296
Pass [Member] \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	387,928		393,710
Financing Receivable, Year One, Originated, Current Fiscal Year	6,841		41,871
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	39,680		54,323
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	$ 52,095		$ 56,102

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