BORROWINGS - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Aug. 02, 2019
Debt Instrument [Line Items]
Residential real estate loans and securities pledged as collateral for FHLB advances, carrying value	$ 451,900	$ 453,200
FHLB Stock owned	10,400	10,400
FHLB borrowing capacity, authorized	800,000
Line of Credit Facility, Current Borrowing Capacity	317,300
Commercial loans pledged as collateral for Federal Reserve Discount Window, carrying value	557,200	446,900
Federal Reserve borrowing capacity	490,400	339,500
Line of Credit Facility, Remaining Borrowing Capacity	350,000	325,000
Outstanding borrowings	10,500
American Financial Exchange [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	394,000	244,000
Unsecured revolving credit agreement
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 30,000
Outstanding borrowings	$ 10,500	$ 0