ACQUISITIONS (Details) shares in Thousands, $ in Thousands								1 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Nov. 01, 2022 USD ($)	May 13, 2022 USD ($) item	Jan. 01, 2022 USD ($)	Aug. 02, 2021 USD ($)	Jul. 01, 2021 USD ($)	Jun. 01, 2021 USD ($)	Jun. 12, 2020 USD ($) country Office shares	Dec. 31, 2022 USD ($) country	Jun. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) country	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Acquisitions
Purchase price of acquisition											$ 85,656
Loans								$ 436,954			436,954
Investment securities								11,305			11,305
Deposits								522,295			522,295
Goodwill								$ 841,841			841,841	$ 799,109	$ 793,708
Provision for credit losses											14,773	(8,839)	14,212
Number of insurance agencies			3
Other intangibles			$ 2,500
Contingent consideration											0
Cash											668	29,329	(34,360)
Acquisition-related contingent consideration adjustment											$ (300)	200	0
Upstate New York
Acquisitions
Number of counties where the bank has facilities | country								42			42
Core deposit intangibles
Acquisitions
Deposits								$ 7,970			$ 7,970
NuVantage Insurance Corp.
Acquisitions
Revenue earned											1,300	700
Direct expenses											1,300	600
Goodwill								42,669			42,669
Cash						$ 2,900
NuVantage Insurance Corp. | Minimum | Adjusted level of retained revenue
Acquisitions
Contingent consideration, measurement input 2								$ 4,900			4,900
Fringe Benefits Design of Minnesota, Inc
Acquisitions
Revenue earned											3,500	2,800
Direct expenses											$ 4,100	2,500
Goodwill					$ 2,100
Period considered for additional consideration based on future retained revenue					2 years
Consideration payable term					3 years
Contingent consideration					$ 1,400
Cash					$ 15,400
Contingent consideration, measurement input					0.0105			0.0609			0.0609
Acquisition-related contingent consideration adjustment									$ 100		$ 500
Fair value contingent consideration adjustment								$ 400			1,100
Increase (decrease) in goodwill as a result of fair value adjustment											(3,600)
Fringe Benefits Design of Minnesota, Inc | Maximum
Acquisitions
Contingent consideration					$ 2,700						2,700
Fringe Benefits Design of Minnesota, Inc | Maximum | Adjusted level of retained revenue
Acquisitions
Contingent consideration, measurement input 2					5,800			$ 5,100			5,100
Fringe Benefits Design of Minnesota, Inc | Minimum
Acquisitions
Contingent consideration					0						0
Fringe Benefits Design of Minnesota, Inc | Minimum | Adjusted level of retained revenue
Acquisitions
Contingent consideration, measurement input 2					5,600
Steuben Trust Corporation
Acquisitions
Revenue earned											11,400	13,100	7,700
Direct expenses											4,800	5,100	2,600
Purchase price of acquisition													98,555
Assets acquired							$ 607,800
Loans							339,700						339,017
Investment securities							180,500						180,497
Deposits							(516,300)						516,274
Goodwill							20,000						19,981
Contingent consideration													0
Cash							$ 98,600
Issuance of common shares (in shares) | shares							1,360
Issuance of common shares							$ 21,600
Increase (decrease) in other liabilities as a result of reclassification and adjustment											(100)
Increase (decrease) in goodwill as a result of fair value adjustment										$ (4,900)
Steuben Trust Corporation | Western New York State
Acquisitions
Number of new counties where the bank has extended footprints | country							2
Number of counties where the bank has facilities | country							4
Number of branch locations | Office							11
Steuben Trust Corporation | Core deposit intangibles
Acquisitions
Deposits													$ 2,928
Thomas Gregory Associates Insurance Brokers, Inc.
Acquisitions
Revenue earned											3,100	600
Direct expenses											1,800	$ 600
Period considered for additional consideration based on future retained revenue				3 years
Contingent consideration				$ 1,500
Acquisition-related contingent consideration adjustment									500		300
Fair value contingent consideration adjustment									$ 200		1,700
Thomas Gregory Associates Insurance Brokers, Inc. | Within two years from acquisition
Acquisitions
Consideration payable term				2 years
Thomas Gregory Associates Insurance Brokers, Inc. | Within three years from acquisition
Acquisitions
Consideration payable term				3 years
Thomas Gregory Associates Insurance Brokers, Inc. | Maximum
Acquisitions
Revenue earned				$ 3,800
Contingent consideration											$ 3,400
Cash				$ 3,400
Contingent consideration, measurement input				0.0109				6.21			6.21
Thomas Gregory Associates Insurance Brokers, Inc. | Maximum | Adjusted level of retained revenue
Acquisitions
Contingent consideration, measurement input 2								$ 3,200			$ 3,200
Thomas Gregory Associates Insurance Brokers, Inc. | Minimum
Acquisitions
Revenue earned				$ 2,300
Contingent consideration											$ 0
Cash				$ 0
Contingent consideration, measurement input				0.0082				5.87			5.87
Thomas Gregory Associates Insurance Brokers, Inc. | Minimum | Adjusted level of retained revenue
Acquisitions
Contingent consideration, measurement input 2								$ 3,100			$ 3,100
Elmira transaction
Acquisitions
Revenue earned											12,100
Direct expenses											3,100
Purchase price of acquisition		$ 82,200									82,179
Number of county | item		5
Assets acquired		$ 583,400
Loans		437,000						436,954			436,954
Investment securities		11,300						11,305			11,305
Deposits		522,300						522,295			522,295
Goodwill		42,200						42,220			42,220
Provision for credit losses		3,900
Contingent consideration											0
Elmira transaction | Core deposit intangibles
Acquisitions
Deposits		$ 8,000						$ 7,970			7,970
OneGroup
Acquisitions
Revenue earned											900
Direct expenses											400
Purchase price of acquisition			$ 2,500
Cash				$ 11,600
Customer list intangible | NuVantage Insurance Corp.
Acquisitions
Other intangibles						1,400
Customer list intangible | Fringe Benefits Design of Minnesota, Inc
Acquisitions
Other intangibles					$ 14,000
Customer list intangible | Thomas Gregory Associates Insurance Brokers, Inc.
Acquisitions
Other intangibles				10,900
Goodwill | NuVantage Insurance Corp.
Acquisitions
Goodwill						$ 1,400
Goodwill | Thomas Gregory Associates Insurance Brokers, Inc.
Acquisitions
Goodwill				$ 2,200
Certain assets of JMD Associates
Acquisitions
Cash paid	$ 1,000
Revenue earned											100
Direct expenses											$ 100
Certain assets of JMD Associates | Noncompete agreement
Acquisitions
Cash paid	100
Certain assets of JMD Associates | Customer list intangible
Acquisitions
Cash paid	400
Certain assets of JMD Associates | Goodwill
Acquisitions
Cash paid	$ 500