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, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities $ 1,929,987 $ 1,893,427
Gross Unrealized Gains 93,394 53,918
Gross Unrealized (Losses) (4,217) (1,900)
Total AFS securities, Estimated Fair Value 2,019,164 1,945,445
U.S. government and agency securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 14,198 21,149
Gross Unrealized Gains 505 209
Gross Unrealized (Losses) (57) (38)
Total AFS securities, Estimated Fair Value 14,646 21,320
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 504,866 421,344
Gross Unrealized Gains 34,968 25,776
Gross Unrealized (Losses) (307) (29)
Total AFS securities, Estimated Fair Value 539,527 447,091
Corporate and other bonds    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 132,489 134,342
Gross Unrealized Gains 1,122 1,991
Gross Unrealized (Losses) (2,261) (374)
Total AFS securities, Estimated Fair Value 131,350 135,959
Commercial    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 357,974 416,904
Gross Unrealized Gains 18,662 8,786
Gross Unrealized (Losses) (88) (643)
Total AFS securities, Estimated Fair Value 376,548 425,047
Commercial | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 337,721 405,731
Gross Unrealized Gains 18,600 8,786
Gross Unrealized (Losses) (88) (619)
Total AFS securities, Estimated Fair Value 356,233 413,898
Commercial | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 20,253 11,173
Gross Unrealized Gains 62  
Gross Unrealized (Losses)   (24)
Total AFS securities, Estimated Fair Value 20,315 11,149
Residential    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 917,361 896,609
Gross Unrealized Gains 38,137 17,156
Gross Unrealized (Losses) (1,504) (816)
Total AFS securities, Estimated Fair Value 953,994 912,949
Residential | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 841,571 852,300
Gross Unrealized Gains 37,643 16,680
Gross Unrealized (Losses) (415) (816)
Total AFS securities, Estimated Fair Value 878,799 868,164
Residential | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 75,790 44,309
Gross Unrealized Gains 494 476
Gross Unrealized (Losses) (1,089)  
Total AFS securities, Estimated Fair Value 75,195 44,785
Other securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 3,099 3,079
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Total AFS securities, Estimated Fair Value $ 3,099 $ 3,079