ACQUISITIONS - Intangible asset, goodwill and acquisition related expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Identifiable Intangible Assets
Merger and acquisition integration related (recoveries) expenses	$ 409	$ 102	$ 4,668	$ 133
Elmira Savings Bank ("Elmira")
Identifiable Intangible Assets
Federal Home Loan Bank of New York borrowings	$ 17,600		$ 17,600
Weighted-average rate	2.48%		2.48%
Elmira Savings Bank ("Elmira") | Core deposit intangibles
Identifiable Intangible Assets
Intangible asset useful life (amortization period)			8 years
NuVantage Insurance Corp. ("NuVantage") | Other intangibles | Second acquisition of 2022 OneGroup
Identifiable Intangible Assets
Intangible asset useful life (amortization period)			8 years
NuVantage Insurance Corp. ("NuVantage") | Other intangibles | Third acquisition of 2022 OneGroup
Identifiable Intangible Assets
Intangible asset useful life (amortization period)			10 years
Thomas Gregory Associates Insurance Brokers, Inc. ("TGA") | Other intangibles
Identifiable Intangible Assets
Intangible asset useful life (amortization period)			13 years
Fringe Benefits Design of Minnesota, Inc ("FBD") | Other intangibles
Identifiable Intangible Assets
Intangible asset useful life (amortization period)			15 years