FAIR VALUE MEASUREMENTS (Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
ASSETS
Securities available for sale, at fair value	$ 3,195,176	$ 2,540,419
Loans held for sale, at fair value	35,417	96,742
LIABILITIES
Fair value hedges	6,769	12,483
Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Securities available for sale, at fair value	64,955	0
Loans held for sale, at fair value	0	0
LIABILITIES
Fair value hedges	0	0
Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	3,130,221	2,540,419
Loans held for sale, at fair value	35,417	96,742
LIABILITIES
Fair value hedges	6,769	12,483
Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0	0
Loans held for sale, at fair value	0	0
LIABILITIES
Fair value hedges	0	0
Recurring
ASSETS
Loans held for sale, at fair value	35,417	96,742
LIABILITIES
Fair value hedges	6,769	12,483
Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Loans held for sale, at fair value	0	0
LIABILITIES
Fair value hedges	0	0
Recurring | Significant Other Observable Inputs Level 2
ASSETS
Loans held for sale, at fair value	35,417	96,742
LIABILITIES
Fair value hedges	6,769	12,483
Recurring | Significant Unobservable Inputs Level 3
ASSETS
Loans held for sale, at fair value	0	0
LIABILITIES
Fair value hedges	0	0
U.S. government and agency securities
ASSETS
Securities available for sale, at fair value	74,818	13,394
U.S. government and agency securities | Recurring
ASSETS
Securities available for sale, at fair value	74,818	13,394
U.S. government and agency securities | Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Securities available for sale, at fair value	64,955	0
U.S. government and agency securities | Recurring | Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	9,863	13,394
U.S. government and agency securities | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0	0
Obligations of states and political subdivisions
ASSETS
Securities available for sale, at fair value	998,881	837,326
Obligations of states and political subdivisions | Recurring
ASSETS
Securities available for sale, at fair value	998,881	837,326
Obligations of states and political subdivisions | Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Securities available for sale, at fair value	0	0
Obligations of states and political subdivisions | Recurring | Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	998,881	837,326
Obligations of states and political subdivisions | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0	0
Corporate and other bonds
ASSETS
Securities available for sale, at fair value	149,028	151,078
Corporate and other bonds | Recurring
ASSETS
Securities available for sale, at fair value	149,028	151,078
Corporate and other bonds | Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Securities available for sale, at fair value	0	0
Corporate and other bonds | Recurring | Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	149,028	151,078
Corporate and other bonds | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0	0
Mortgage-backed securities | Recurring
ASSETS
Securities available for sale, at fair value	1,970,813	1,536,996
Mortgage-backed securities | Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Securities available for sale, at fair value	0	0
Mortgage-backed securities | Recurring | Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	1,970,813	1,536,996
Mortgage-backed securities | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0	0
Other securities
ASSETS
Securities available for sale, at fair value	1,636	1,625
Other securities | Recurring
ASSETS
Securities available for sale, at fair value	1,636	1,625
Other securities | Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Securities available for sale, at fair value	0	0
Other securities | Recurring | Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	1,636	1,625
Other securities | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0	0
Interest Rate Swap
ASSETS
Interest rate swap	90,246	163,360
LIABILITIES
Interest rate swap	52,096	163,360
Interest Rate Swap | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Interest rate swap	0	0
LIABILITIES
Interest rate swap	0	0
Interest Rate Swap | Significant Other Observable Inputs Level 2
ASSETS
Interest rate swap	90,246	163,360
LIABILITIES
Interest rate swap	52,096	163,360
Interest Rate Swap | Significant Unobservable Inputs Level 3
ASSETS
Interest rate swap	0	0
LIABILITIES
Interest rate swap	0	0
Interest Rate Swap | Recurring
ASSETS
Interest rate swap	90,246	163,360
LIABILITIES
Interest rate swap	52,096	163,360
Interest Rate Swap | Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Interest rate swap	0	0
LIABILITIES
Interest rate swap	0	0
Interest Rate Swap | Recurring | Significant Other Observable Inputs Level 2
ASSETS
Interest rate swap	90,246	163,360
LIABILITIES
Interest rate swap	52,096	163,360
Interest Rate Swap | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Interest rate swap	0	0
LIABILITIES
Interest rate swap	$ 0	$ 0