SECURITIES (Amortized Cost of AFS Securities by Security Type and Credit Rating) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	$ 1,929,987	$ 1,893,427
U.S. government and agency securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	14,198	21,149
Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	504,866	421,344
Corporate and other bonds
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	132,489	134,342
Other securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
AFS Securities, Amortized Cost	$ 3,099	$ 3,079