ACQUISITIONS - Supplemental Pro Forma Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Business acquisition
Total revenue, net of interest expense, pro forma	$ 687,976	$ 646,375	$ 607,382
Net income, pro forma	193,417	$ 191,450	171,147
Steuben Trust Corporation
Business acquisition
Acquisitions-related expenses			$ 4,800
Elmira transaction
Business acquisition
Acquisitions-related expenses	$ 5,000