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
Jun. 30, 2019
Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities $ 1,949,679 $ 1,780,952
Gross Unrealized Gains 51,764 9,414
Gross Unrealized (Losses) (1,949) (15,545)
Estimated Fair Value 1,999,494 1,774,821
U.S. government and agency securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 4,462  
Gross Unrealized Gains 18  
Gross Unrealized (Losses) 0  
Estimated Fair Value 4,480  
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 485,192 466,588
Gross Unrealized Gains 24,566 3,844
Gross Unrealized (Losses) (11) (1,941)
Estimated Fair Value 509,747 468,491
Corporate and other bonds    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 202,935 167,561
Gross Unrealized Gains 3,887 1,118
Gross Unrealized (Losses) (509) (983)
Estimated Fair Value 206,313 167,696
Mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 1,253,541 1,138,034
Gross Unrealized Gains 23,293 4,452
Gross Unrealized (Losses) (1,429) (12,621)
Estimated Fair Value 1,275,405 1,129,865
Other securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 3,549 8,769
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Estimated Fair Value $ 3,549 $ 8,769