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ACQUISITIONS (Details) shares in Thousands, $ in Thousands					3 Months Ended			6 Months Ended
	Jun. 12, 2020 USD ($) Branch County shares	Sep. 18, 2019 USD ($)	Jul. 12, 2019 USD ($) Branch County	Jan. 02, 2019 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Acquisitions [Abstract]
Cash		$ 500	$ 95,034
Loans acquired								$ 339,692
Investment securities			39,770
Increase in deposits								1,335,437	$ 165,834
Customer Lists [Member]
Acquisitions [Abstract]
Intangibles		$ 500
Steuben [Member]
Acquisitions [Abstract]
Issuance of common shares (in shares) | shares	1,360
Cash	$ 21,613
Assets acquired	610,100
Loans acquired	339,700
Investment securities	$ 180,497
Revenues					$ 600			600
Direct expenses					300			300
Steuben [Member] | Western New York State [Member]
Acquisitions [Abstract]
Number of counties where the bank has facilities | County	4
Number of new counties where the bank has extended footprints | County	2
Number of branch locations | Branch	11
Kinderhook Bank Corp [Member]
Acquisitions [Abstract]
Cash			$ 93,384
Number of branch locations | Branch			11
Investment securities			$ 39,770
Increase in deposits							$ 80
Decrease in loans							(50)
Increase (decrease) in other liabilities as a result of reclassification and adjustment						$ (300)	40
Decrease in other assets							(40)
Increased in accrued interest and fees receivable							10
Increase (decrease) in goodwill as a result of fair value adjustment						$ (300)	$ 200
Kinderhook Bank Corp [Member] | Upstate New York [Member]
Acquisitions [Abstract]
Number of counties where the bank has facilities | County			5
Assets acquired			$ 642,800
Investment securities			$ 39,800
Revenues					4,400			8,900
Direct expenses					$ 1,700			$ 3,600
Wealth Resources Network, Inc [Member]
Acquisitions [Abstract]
Cash				$ 1,200
Wealth Resources Network, Inc [Member] | Customer Lists [Member]
Acquisitions [Abstract]
Intangibles				$ 1,200

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