ACQUISITION - PRO FORMA INFORMATION (Details) - SI Financial Group, Inc. - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Net interest income	$ 383,828	$ 412,164
Non-interest income	88,500	85,563
Income available to common shareholders	$ 118,552	$ 127,693

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