BORROWED FUNDS - Short-term borrowings - Additional information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
BORROWED FUNDS
Short-term Debt, Weighted Average Interest Rate, at Point in Time		0.10%	5.23%
Short-term borrowings		$ 2,488,000	$ 33,874,000
Line of Credit Facility, Maximum Month-end Outstanding Amount		61,936,000	120,290,000	$ 90,042,000
Other Assets [Member]
BORROWED FUNDS
Federal Home Loan Bank Stock		6,299,000	6,252,000
Other Correspondent Banks
BORROWED FUNDS
Line of Credit Facility, Maximum Borrowing Capacity		75,000,000
Long-term Line of Credit, Total		0	0
Federal Reserve Bank of Philadelphia | Collateral Pledged
BORROWED FUNDS
Investment pledged as collateral		$ 18,881,000	$ 20,829,000
Customer repurchase agreements
BORROWED FUNDS
Debt, Weighted Average Interest Rate		0.10%	0.10%
Carrying Value of Securities Sold under Repurchase Agreements and Deposits Received for Securities Loaned, Total		$ 2,500,000	$ 2,400,000
Short-term borrowings		2,488,000	2,374,000
FHLB-Pittsburgh borrowings
BORROWED FUNDS
Short-term borrowings		0	31,500,000
Federal Home Loan Bank of Pittsburgh
BORROWED FUNDS
Line of Credit Facility, Maximum Borrowing Capacity		938,691,000	926,845,000
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged		1,351,770,000	1,323,008,000
Line of Credit Facility, Remaining Borrowing Capacity		749,999,000	737,824,000
Federal Home Loan Bank of Pittsburgh | Other Assets [Member]
BORROWED FUNDS
Federal Home Loan Bank Stock		15,018,000	15,214,000
Federal Home Loan Bank of Pittsburgh | Federal Reserve Bank of Philadelphia
BORROWED FUNDS
Line of Credit Facility, Maximum Borrowing Capacity		18,093,000	19,982,000
Long-term Line of Credit, Total		0	0
Federal Home Loan Bank of Pittsburgh | Overnight Borrowing
BORROWED FUNDS
Short-term borrowings		$ 0	$ 6,500,000
Overnight interest rate			5.68%
Weighted average interest rate	5.60%
Federal Home Loan Bank of Pittsburgh | FHLB-Pittsburgh borrowings
BORROWED FUNDS
Short-term borrowings			$ 25,000,000