Quarterly report pursuant to Section 13 or 15(d)

SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details)

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SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities $ 1,859,349 $ 1,780,952
Gross Unrealized Gains 60,866 9,414
Gross Unrealized (Losses) (1,356) (15,545)
Estimated Fair Value 1,918,859 1,774,821
U.S. government and agency securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 4,475  
Gross Unrealized Gains 15  
Gross Unrealized (Losses) 0  
Estimated Fair Value 4,490  
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 411,690 466,588
Gross Unrealized Gains 26,935 3,844
Gross Unrealized (Losses) (12) (1,941)
Estimated Fair Value 438,613 468,491
Corporate and other bonds    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 224,854 167,561
Gross Unrealized Gains 5,044 1,118
Gross Unrealized (Losses) (374) (983)
Estimated Fair Value 229,524 167,696
Mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 1,215,263 1,138,034
Gross Unrealized Gains 28,872 4,452
Gross Unrealized (Losses) (970) (12,621)
Estimated Fair Value 1,243,165 1,129,865
Other securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 3,067 8,769
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Estimated Fair Value $ 3,067 $ 8,769