ACQUISITIONS - Estimated fair value of assets acquired and liabilities (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
	May 13, 2022	Sep. 30, 2023	Dec. 31, 2022	Mar. 01, 2023	Sep. 30, 2022
Consideration :
Cash		$ 8,301	$ 85,656
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents		0	84,988
Investment securities		0	11,305
Loans, net of allowance for credit losses on PCD loans		0	436,796
Premises and equipment, net		66	11,317
Accrued interest and fees receivable		0	882
Other assets		177	30,337
Deposits		0	(522,295)
Other liabilities		(18)	(3,630)
Other Federal Home Loan Bank borrowings		0	(17,616)
Total identifiable assets, net		6,115	43,068
Contingent consideration		1,450	0
Total net consideration		9,751	85,656
Goodwill		845,396	841,841		$ 844,984
Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits		0	7,970
Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles		5,890	3,014
Axiom
Consideration :
Cash		1,819
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		25
Accrued interest and fees receivable		0
Other assets		2
Deposits		0
Other intangibles				$ 1,200
Other liabilities		(9)
Other Federal Home Loan Bank borrowings		0
Total identifiable assets, net		1,194
Contingent consideration		0
Total net consideration		1,819
Goodwill		625		$ 600
Axiom | Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits		0
Axiom | Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles		1,176
Elmira acquisition
Consideration :
Cash			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	436,800		436,796
Premises and equipment, net			11,303
Accrued interest and fees receivable			882
Other assets			30,337
Deposits	(522,300)		(522,295)
Other liabilities			(3,596)
Other Federal Home Loan Bank borrowings			(17,616)
Total identifiable assets, net			40,074
Contingent consideration			0
Total net consideration	82,200		82,179
Goodwill	42,100		42,105
Elmira acquisition | Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits	$ (8,000)		7,970
Elmira acquisition | Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles			0
Other
Consideration :
Cash		6,482	3,477
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash and cash equivalents		0	0
Investment securities		0	0
Loans, net of allowance for credit losses on PCD loans		0	0
Premises and equipment, net		41	14
Accrued interest and fees receivable		0	0
Other assets		175	0
Deposits		0	0
Other liabilities		(9)	(34)
Other Federal Home Loan Bank borrowings		0	0
Total identifiable assets, net		4,921	2,994
Contingent consideration		1,450	0
Total net consideration		7,932	3,477
Goodwill		3,011	483
Other | Core deposit intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Deposits		0	0
Other | Other intangibles
Recognized amounts of identifiable assets acquired and liabilities assumed:
Other intangibles		4,714	3,014
One Group Acquisitions
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill		$ 3,636	$ 42,588