LOANS AND ALLOWANCE FOR CREDIT LOSSES - Loan Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Loans receivable, net
Gross loans, including deferred origination costs	$ 8,809,394	$ 7,373,639
Allowance for credit losses	(61,059)	(49,869)
Net loans	8,748,335	7,323,770
Net deferred loan origination costs	73,800	34,900
Loans receivable, related parties
Balance at beginning of year	13,773	15,549
New loans	2,025	2,500
Payments	(3,425)	(4,276)
Balance at end of year	12,373	13,773
Business Lending
Loans receivable, net
Gross loans, including deferred origination costs	3,645,665	3,075,904
Consumer Mortgage
Loans receivable, net
Gross loans, including deferred origination costs	3,012,475	2,556,114
Consumer Indirect
Loans receivable, net
Gross loans, including deferred origination costs	1,539,653	1,189,749
Consumer Direct
Loans receivable, net
Gross loans, including deferred origination costs	177,605	153,811
Home Equity
Loans receivable, net
Gross loans, including deferred origination costs	433,996	398,061
Allowance for credit losses				$ (2,129)
Commercial Portfolio Segment | Business Lending
Loans receivable, net
Gross loans, including deferred origination costs	3,645,665	3,075,904
Allowance for credit losses		(22,995)	$ (30,072)	(19,426)
Commercial Portfolio Segment | Consumer Mortgage
Loans receivable, net
Allowance for credit losses		(10,017)	(10,672)	(10,269)
Residential Portfolio Segment | Consumer Mortgage
Loans receivable, net
Gross loans, including deferred origination costs	3,012,475	2,556,114
Consumer Portfolio Segment | Business Lending
Loans receivable, net
Allowance for credit losses	(23,297)	(22,995)
Consumer Portfolio Segment | Consumer Mortgage
Loans receivable, net
Allowance for credit losses	(14,343)	(10,017)
Consumer Portfolio Segment | Consumer Indirect
Loans receivable, net
Gross loans, including deferred origination costs	1,539,653	1,189,749
Allowance for credit losses	(17,852)	(11,737)	(13,696)	(13,712)
Consumer Portfolio Segment | Consumer Direct
Loans receivable, net
Gross loans, including deferred origination costs	177,605	153,811
Allowance for credit losses	(2,973)	(2,306)	(3,207)	$ (3,255)
Consumer Portfolio Segment | Home Equity
Loans receivable, net
Gross loans, including deferred origination costs	433,996	398,061
Allowance for credit losses	$ (1,594)	$ (1,814)	$ (2,222)