SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) item segment component country subsidiary Office	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Nature of Operations [Abstract]
Number of significant consolidated subsidiaries owned | subsidiary	2
Number of bank branches | Office	206
Number Of Operating Location | item	12
Risks and Uncertainties [Abstract]
Number of main components of economic risk | component	3
Wealth Management Services [Abstract]
Number of types of performance obligations | item	2
Contract Balances [Abstract]
Accounts receivable	$ 31.6	$ 30.3
Unbilled fee revenue	9.1	7.7
Unearned revenue	2.2	1.4
Cash and Cash Equivalents [Abstract]
Cash due from banks	11.0	7.7
Allowance for Loan Losses [Abstract]
Accrued interest and fees receivable	16.7	22.2
Other Real Estate [Abstract]
Other real estate	0.7	0.9
Investments in Real Estate Limited Partnerships [Abstract]
Unfunded commitments	0.2
Impairment losses related to real estate partnerships	0.0
Advertising [Abstract]
Advertising costs	5.2	6.1	$ 7.1
Available-for-sale Securities [Member]
Allowance for Loan Losses [Abstract]
Accrued interest and fees receivable	$ 15.8	$ 13.3
Land Improvements [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	20 years
Minimum | LIHTC [Member]
Investments in Real Estate Limited Partnerships [Abstract]
Ownership interest	5.00%
Minimum | Equipment [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	2 years
Minimum | Software [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	3 years
Minimum | Hardware [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	3 years
Minimum | Building and Building Improvements [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	10 years
Minimum | Core deposit intangibles
Intangible Assets [Abstract]
Intangible asset useful life (amortization period)	7 years
Minimum | Customer Relationships [Member]
Intangible Assets [Abstract]
Intangible asset useful life (amortization period)	7 years
Maximum
Impaired and Other Nonaccrual Loans [Abstract]
Threshold balance of loans individually evaluated for impairment	$ 0.5
Maximum | LIHTC [Member]
Investments in Real Estate Limited Partnerships [Abstract]
Ownership interest	99.99%
Maximum | Equipment [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	20 years
Maximum | Software [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	7 years
Maximum | Hardware [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	7 years
Maximum | Building and Building Improvements [Member]
Property, Plant and Equipment, Gross [Abstract]
Estimated useful life	40 years
Maximum | Core deposit intangibles
Intangible Assets [Abstract]
Intangible asset useful life (amortization period)	20 years
Maximum | Customer Relationships [Member]
Intangible Assets [Abstract]
Intangible asset useful life (amortization period)	20 years
BPAS [Member]
Nature of Operations [Abstract]
Number of significant consolidated subsidiaries owned | segment	5
Hand Benefits & Trust [Member]
Nature of Operations [Abstract]
Number of significant consolidated subsidiaries owned | segment	1
NRS [Member]
Nature of Operations [Abstract]
Number of significant consolidated subsidiaries owned | segment	1
Upstate New York.
Nature of Operations [Abstract]
Number of counties where the bank has facilities | country	42
PENNSYLVANIA
Nature of Operations [Abstract]
Number of counties where the bank has facilities | country	6
Vermont [Member]
Nature of Operations [Abstract]
Number of counties where the bank has facilities | country	12
Massachusetts [Member]
Nature of Operations [Abstract]
Number of counties where the bank has facilities | country	1