FAIR VALUE MEASUREMENTS (Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
ASSETS
Securities available for sale, at fair value	$ 1,972,903	$ 1,945,445
Loans held for sale, at fair value	76,690	55,405
Fair value hedges	1	182
LIABILITIES
Cash flow hedges		1,147
Fair value hedges	14,769	6,256
Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Securities available for sale, at fair value	0	0
Loans held for sale, at fair value	0	0
Fair value hedges	0	0
LIABILITIES
Cash flow hedges		0
Fair value hedges	0	0
Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	1,972,903	1,945,445
Loans held for sale, at fair value	76,690	55,405
Fair value hedges	1	182
LIABILITIES
Cash flow hedges		1,147
Fair value hedges	14,769	6,256
Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0	0
Loans held for sale, at fair value	0	0
Fair value hedges	0	0
LIABILITIES
Cash flow hedges		0
Fair value hedges	0	0
Recurring
ASSETS
Loans held for sale, at fair value	76,690	55,405
Fair value hedges	1	182
LIABILITIES
Cash flow hedges		1,147
Fair value hedges	14,769	6,256
Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Loans held for sale, at fair value	0	0
Fair value hedges	0	0
LIABILITIES
Cash flow hedges		0
Fair value hedges	0	0
Recurring | Significant Other Observable Inputs Level 2
ASSETS
Loans held for sale, at fair value	76,690	55,405
Fair value hedges	1	182
LIABILITIES
Cash flow hedges		1,147
Fair value hedges	14,769	6,256
Recurring | Significant Unobservable Inputs Level 3
ASSETS
Loans held for sale, at fair value	0	0
Fair value hedges	0	0
LIABILITIES
Cash flow hedges		0
Fair value hedges	0	0
U.S. government and agency securities
ASSETS
Securities available for sale, at fair value	17,962	21,320
U.S. government and agency securities | Recurring
ASSETS
Securities available for sale, at fair value	17,962	21,320
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	0
U.S. government and agency securities | Recurring | Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	17,962	21,320
U.S. government and agency securities | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0
Obligations of states and political subdivisions
ASSETS
Securities available for sale, at fair value	546,726	447,091
Obligations of states and political subdivisions | Recurring
ASSETS
Securities available for sale, at fair value	546,726	447,091
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	546,726	447,091
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	120,968	135,959
Corporate and other bonds | Recurring
ASSETS
Securities available for sale, at fair value	120,968	135,959
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	120,968	135,959
Corporate and other bonds | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Securities available for sale, at fair value	0	0
Total mortgage-back securities
ASSETS
Securities available for sale, at fair value	1,284,157	1,337,996
Total mortgage-back securities | Recurring
ASSETS
Securities available for sale, at fair value	1,284,157	1,337,996
Total mortgage-back securities | Recurring | Quoted Prices in Active Markets for Identical Assets Level 1
ASSETS
Securities available for sale, at fair value	0	0
Total mortgage-back securities | Recurring | Significant Other Observable Inputs Level 2
ASSETS
Securities available for sale, at fair value	1,284,157	1,337,996
Total mortgage-back 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	3,090	3,079
Other securities | Recurring
ASSETS
Securities available for sale, at fair value	3,090	3,079
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	3,090	3,079
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	174,704	54,345
LIABILITIES
Interest rate swap	174,704	54,345
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	174,704	54,345
LIABILITIES
Interest rate swap	174,704	54,345
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	174,704	54,345
LIABILITIES
Interest rate swap	174,704	54,345
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	174,704	54,345
LIABILITIES
Interest rate swap	174,704	54,345
Interest Rate Swap | Recurring | Significant Unobservable Inputs Level 3
ASSETS
Interest rate swap	0	0
LIABILITIES
Interest rate swap	$ 0	$ 0