ACQUISITIONS - Estimated fair value of assets acquired and liabilities assumed (Details) - USD ($) $ in Thousands				9 Months Ended	12 Months Ended
	May 13, 2022	Aug. 02, 2021	Jul. 01, 2021	Sep. 30, 2022	Dec. 31, 2021	Jan. 01, 2022	Sep. 30, 2021
Consideration :
Cash				$ 84,643	$ 29,870
Contingent consideration				0	2,900
Total net consideration				84,643	32,770
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents				84,988	541
Investment securities				11,305	0
Loans, net of allowance for credit losses on PCD loans				436,948	0
Premises and equipment, net				11,303	760
Accrued interest and fees receivable				884	0
Other assets				25,637	579
Other intangibles						$ 2,500
Deposits				(522,295)	0
Other liabilities				(2,757)	(1,164)
Other Federal Home Loan Bank borrowings				(17,616)	0
Total identifiable assets, net				38,831	27,053
Goodwill				844,984	799,109		$ 799,127
Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits				7,970	0
Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles				2,464	26,337
Elmira Savings Bank ("Elmira")
Consideration :
Cash				82,179
Contingent consideration				0
Total net consideration	$ 82,200			82,179
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents				84,988
Investment securities	11,300			11,305
Loans, net of allowance for credit losses on PCD loans	437,000			436,948
Premises and equipment, net				11,303
Accrued interest and fees receivable				884
Other assets				25,637
Deposits	(522,300)			(522,295)
Other liabilities				(2,757)
Other Federal Home Loan Bank borrowings				(17,616)
Total identifiable assets, net				36,367
Goodwill	45,800			45,812
Elmira Savings Bank ("Elmira") | Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits	$ (8,000)			7,970
Elmira Savings Bank ("Elmira") | Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles				0
Other
Consideration :
Cash				2,464
Contingent consideration				0
Total net consideration				2,464
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents				0
Investment securities				0
Loans, net of allowance for credit losses on PCD loans				0
Premises and equipment, net				0
Accrued interest and fees receivable				0
Other assets				0
Deposits				0
Other liabilities				0
Other Federal Home Loan Bank borrowings				0
Total identifiable assets, net				2,464
Goodwill				0
Other | Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits				0
Other | Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles				2,464
Thomas Gregory Associates Insurance Brokers, Inc. ("TGA")
Consideration :
Cash					11,620
Contingent consideration		$ 1,500			1,500
Total net consideration					13,120
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents					0
Investment securities					0
Loans, net of allowance for credit losses on PCD loans					0
Premises and equipment, net					279
Accrued interest and fees receivable					0
Other assets					0
Deposits					0
Other liabilities					(229)
Other Federal Home Loan Bank borrowings					0
Total identifiable assets, net					10,950
Goodwill		$ 2,200			2,170
Thomas Gregory Associates Insurance Brokers, Inc. ("TGA") | Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits					0
Thomas Gregory Associates Insurance Brokers, Inc. ("TGA") | Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles					10,900
Fringe Benefits Design of Minnesota, Inc ("FBD")
Consideration :
Cash					15,350
Contingent consideration			$ 1,400		1,400
Total net consideration					16,750
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents					541
Investment securities					0
Loans, net of allowance for credit losses on PCD loans					0
Premises and equipment, net					282
Accrued interest and fees receivable					0
Other assets					579
Deposits					0
Other liabilities					(761)
Other Federal Home Loan Bank borrowings					0
Total identifiable assets, net					14,641
Goodwill			$ 2,100		2,109
Fringe Benefits Design of Minnesota, Inc ("FBD") | Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits					0
Fringe Benefits Design of Minnesota, Inc ("FBD") | Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles					14,000
NuVantage
Consideration :
Cash					2,900
Contingent consideration					0
Total net consideration					2,900
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents					0
Investment securities					0
Loans, net of allowance for credit losses on PCD loans					0
Premises and equipment, net					199
Accrued interest and fees receivable					0
Other assets					0
Deposits					0
Other liabilities					(174)
Other Federal Home Loan Bank borrowings					0
Total identifiable assets, net					1,462
Goodwill					1,438
NuVantage | Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits					0
NuVantage | Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles					1,437
One Group Acquisitions
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill				$ 45,812	$ 5,717