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, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities $ 2,352,916 $ 1,893,427
Gross Unrealized Gains 95,593 53,918
Gross Unrealized (Losses) (5,169) (1,900)
Total AFS securities, Estimated Fair Value 2,443,340 1,945,445
U.S. government and agency securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 13,463 21,149
Gross Unrealized Gains 465 209
Gross Unrealized (Losses) (50) (38)
Total AFS securities, Estimated Fair Value 13,878 21,320
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 759,936 421,344
Gross Unrealized Gains 39,033 25,776
Gross Unrealized (Losses) (2,113) (29)
Total AFS securities, Estimated Fair Value 796,856 447,091
Corporate and other bonds    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 147,438 134,342
Gross Unrealized Gains 2,217 1,991
Gross Unrealized (Losses) (737) (374)
Total AFS securities, Estimated Fair Value 148,918 135,959
Commercial    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 371,065 416,904
Gross Unrealized Gains 18,016 8,786
Gross Unrealized (Losses) (116) (643)
Total AFS securities, Estimated Fair Value 388,965 425,047
Commercial | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 340,706 405,731
Gross Unrealized Gains 17,945 8,786
Gross Unrealized (Losses) (116) (619)
Total AFS securities, Estimated Fair Value 358,535 413,898
Commercial | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 30,359 11,173
Gross Unrealized Gains 71  
Gross Unrealized (Losses)   (24)
Total AFS securities, Estimated Fair Value 30,430 11,149
Residential    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,059,393 896,609
Gross Unrealized Gains 35,862 17,156
Gross Unrealized (Losses) (2,153) (816)
Total AFS securities, Estimated Fair Value 1,093,102 912,949
Residential | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 960,141 852,300
Gross Unrealized Gains 35,275 16,680
Gross Unrealized (Losses) (1,410) (816)
Total AFS securities, Estimated Fair Value 994,006 868,164
Residential | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 99,252 44,309
Gross Unrealized Gains 587 476
Gross Unrealized (Losses) (743)  
Total AFS securities, Estimated Fair Value 99,096 44,785
Other securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,621 3,079
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Total AFS securities, Estimated Fair Value $ 1,621 $ 3,079