SECURITIES (Amortized Cost of AFS Securities by Security Type and Credit Rating) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	$ 2,352,916	$ 1,893,427
U.S. government and agency securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	13,463	21,149
Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	759,936	421,344
Corporate and other bonds
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	147,438	134,342
Other securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	$ 1,621	$ 3,079