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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
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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

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