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, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities $ 2,439,247 $ 1,893,427
Gross Unrealized Gains 103,512 53,918
Gross Unrealized (Losses) (2,340) (1,900)
Total AFS securities, Estimated Fair Value 2,540,419 1,945,445
U.S. government and agency securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 13,009 21,149
Gross Unrealized Gains 437 209
Gross Unrealized (Losses) (52) (38)
Total AFS securities, Estimated Fair Value 13,394 21,320
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 786,466 421,344
Gross Unrealized Gains 50,878 25,776
Gross Unrealized (Losses) (18) (29)
Total AFS securities, Estimated Fair Value 837,326 447,091
Corporate and other bonds    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 148,747 134,342
Gross Unrealized Gains 2,430 1,991
Gross Unrealized (Losses) (99) (374)
Total AFS securities, Estimated Fair Value 151,078 135,959
Commercial    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 372,259 416,904
Gross Unrealized Gains 16,444 8,786
Gross Unrealized (Losses) (19) (643)
Total AFS securities, Estimated Fair Value 388,684 425,047
Commercial | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 321,015 405,731
Gross Unrealized Gains 16,277 8,786
Gross Unrealized (Losses) (2) (619)
Total AFS securities, Estimated Fair Value 337,290 413,898
Commercial | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 51,244 11,173
Gross Unrealized Gains 167 0
Gross Unrealized (Losses) (17) (24)
Total AFS securities, Estimated Fair Value 51,394 11,149
Residential    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,117,141 896,609
Gross Unrealized Gains 33,323 17,156
Gross Unrealized (Losses) (2,152) (816)
Total AFS securities, Estimated Fair Value 1,148,312 912,949
Residential | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,012,237 852,300
Gross Unrealized Gains 31,816 16,680
Gross Unrealized (Losses) (1,946) (816)
Total AFS securities, Estimated Fair Value 1,042,107 868,164
Residential | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 104,904 44,309
Gross Unrealized Gains 1,507 476
Gross Unrealized (Losses) (206) 0
Total AFS securities, Estimated Fair Value 106,205 44,785
Other securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,625 3,079
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Total AFS securities, Estimated Fair Value $ 1,625 $ 3,079