Annual report pursuant to Section 13 and 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
Dec. 31, 2018
Dec. 31, 2017
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total securities available for sale, Amortized Cost $ 1,780,952 $ 971,339
Gross Unrealized Gains 9,414 10,569
Gross Unrealized (Losses) (15,545) (7,686)
Available for sale securities, Estimated fair value 1,774,821 974,222
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total securities available for sale, Amortized Cost 466,588 295,546
Gross Unrealized Gains 3,844 6,842
Gross Unrealized (Losses) (1,941) (564)
Available for sale securities, Estimated fair value 468,491 301,824
Corporate bonds    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total securities available for sale, Amortized Cost 167,561 113,625
Gross Unrealized Gains 1,118 1,131
Gross Unrealized (Losses) (983) (876)
Available for sale securities, Estimated fair value 167,696 113,880
Mortgage-backed securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total securities available for sale, Amortized Cost 1,138,034 552,431
Gross Unrealized Gains 4,452 2,596
Gross Unrealized (Losses) (12,621) (6,169)
Available for sale securities, Estimated fair value 1,129,865 548,858
Other securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total securities available for sale, Amortized Cost 8,769 9,737
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 (77)
Available for sale securities, Estimated fair value $ 8,769 $ 9,660