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
Mar. 31, 2019
Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities $ 2,088,851 $ 1,780,952
Gross Unrealized Gains 27,227 9,414
Gross Unrealized (Losses) (7,016) (15,545)
Estimated Fair Value 2,109,062 1,774,821
U.S. government and agency securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 4,451  
Gross Unrealized Gains 6  
Gross Unrealized (Losses) 0  
Estimated Fair Value 4,457  
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 516,897 466,588
Gross Unrealized Gains 14,972 3,844
Gross Unrealized (Losses) (81) (1,941)
Estimated Fair Value 531,788 468,491
Corporate and other bonds    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 177,910 167,561
Gross Unrealized Gains 1,784 1,118
Gross Unrealized (Losses) (807) (983)
Estimated Fair Value 178,887 167,696
Mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 1,386,056 1,138,034
Gross Unrealized Gains 10,465 4,452
Gross Unrealized (Losses) (6,128) (12,621)
Estimated Fair Value 1,390,393 1,129,865
Other securities    
Debt Securities, Available-for-sale [Line Items]    
Total AFS securities 3,537 8,769
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Estimated Fair Value $ 3,537 $ 8,769