SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) item component	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2023 subsidiary	Dec. 31, 2023 segment	Dec. 31, 2023 Office	Dec. 31, 2023 item	Dec. 31, 2023 country	Dec. 31, 2023 USD ($)	Dec. 31, 2023
Nature of Operations
Number of significant consolidated subsidiaries owned				2	5
Number of bank branches | Office						193
Number Of Operating Location | item	12
Risk and Uncertainties
Number of main components of economic risk | component	3
Wealth Management Services
Number of types of performance obligations | item							2
Contract Balances
Contract with Customer, Asset, after Allowance for Credit Loss		$ 33.3							$ 41.7
Unbilled Contracts Receivable		8.8							8.1
Revenue, Remaining Performance Obligation, Amount		1.1							0.8
Cash and Cash Equivalents
Cash due from banks		10.0							11.5
Allowance for Loan Losses
Accrued interest and fees receivable		4.7							5.0
Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Interest Receivable
Other Real Estate
Other real estate		0.5							1.2
Investments in Real Estate Limited Partnerships
Impairment losses related to real estate partnerships	$ 0.0
Advertising
Advertising costs	$ 9.5	8.2	$ 5.2
Available-for-sale Securities
Allowance for Loan Losses
Accrued interest and fees receivable		19.3							14.4
Accrued interest receivable on held-to-maturity securities, included in accrued interest and fees receivable		$ 4.7							$ 5.0
Land Improvements
Property, Plant and Equipment, Gross
Estimated useful life	20 years
Minimum | LITCH
Investments in Real Estate Limited Partnerships
Ownership interest										5.00%
Minimum | Premises and Equipment
Property, Plant and Equipment, Gross
Estimated useful life	2 years
Minimum | Software
Property, Plant and Equipment, Gross
Estimated useful life	3 years
Minimum | Hardware
Property, Plant and Equipment, Gross
Estimated useful life	3 years
Minimum | Building and Building Improvements
Property, Plant and Equipment, Gross
Estimated useful life	10 years
Minimum | Core deposit intangibles
Intangible Assets
Finite-Lived Intangible Asset, Useful Life	7 years
Minimum | Customer relationships
Intangible Assets
Finite-Lived Intangible Asset, Useful Life	7 years
Maximum | LITCH
Investments in Real Estate Limited Partnerships
Ownership interest										99.99%
Maximum | Premises and Equipment
Property, Plant and Equipment, Gross
Estimated useful life	20 years
Maximum | Software
Property, Plant and Equipment, Gross
Estimated useful life	7 years
Maximum | Hardware
Property, Plant and Equipment, Gross
Estimated useful life	7 years
Maximum | Building and Building Improvements
Property, Plant and Equipment, Gross
Estimated useful life	40 years
Maximum | Core deposit intangibles
Intangible Assets
Finite-Lived Intangible Asset, Useful Life	20 years
Maximum | Customer relationships
Intangible Assets
Finite-Lived Intangible Asset, Useful Life	20 years
BPAS
Nature of Operations
Number of significant consolidated subsidiaries owned | segment					1
Hand Benefits & Trust
Nature of Operations
Number of significant consolidated subsidiaries owned | segment					1
NRS
Nature of Operations
Number of significant consolidated subsidiaries owned | segment					1
Upstate New York.
Nature of Operations
Number of counties where the bank has facilities | country								42
Northeastern Pennsylvania
Nature of Operations
Number of counties where the bank has facilities | country								6
Vermont
Nature of Operations
Number of counties where the bank has facilities | country								12
Western Massachusetts
Nature of Operations
Number of counties where the bank has facilities | country								1