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
Mar. 31, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities $ 2,640,063 $ 2,439,247
Gross Unrealized Gains 78,131 103,512
Gross Unrealized (Losses) (21,151) (2,340)
Total AFS securities, Estimated Fair Value 2,697,043 2,540,419
U.S. government and agency securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 11,470 13,009
Gross Unrealized Gains 254 437
Gross Unrealized (Losses) (47) (52)
Total AFS securities, Estimated Fair Value 11,677 13,394
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 868,297 786,466
Gross Unrealized Gains 35,757 50,878
Gross Unrealized (Losses) (4,956) (18)
Total AFS securities, Estimated Fair Value 899,098 837,326
Corporate and other bonds    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 145,403 148,747
Gross Unrealized Gains 2,448 2,430
Gross Unrealized (Losses) (243) (99)
Total AFS securities, Estimated Fair Value 147,608 151,078
Commercial    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 375,218 372,259
Gross Unrealized Gains 11,339 16,444
Gross Unrealized (Losses) (1,725) (19)
Total AFS securities, Estimated Fair Value 384,832 388,684
Commercial | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 316,527 321,015
Gross Unrealized Gains 11,260 16,277
Gross Unrealized (Losses) (1,615) (2)
Total AFS securities, Estimated Fair Value 326,172 337,290
Commercial | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 58,691 51,244
Gross Unrealized Gains 79 167
Gross Unrealized (Losses) (110) (17)
Total AFS securities, Estimated Fair Value 58,660 51,394
Residential    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,238,050 1,117,141
Gross Unrealized Gains 28,333 33,323
Gross Unrealized (Losses) (14,180) (2,152)
Total AFS securities, Estimated Fair Value 1,252,203 1,148,312
Residential | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,138,014 1,012,237
Gross Unrealized Gains 26,812 31,816
Gross Unrealized (Losses) (13,668) (1,946)
Total AFS securities, Estimated Fair Value 1,151,158 1,042,107
Residential | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 100,036 104,904
Gross Unrealized Gains 1,521 1,507
Gross Unrealized (Losses) (512) (206)
Total AFS securities, Estimated Fair Value 101,045 106,205
Other securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,625 1,625
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Total AFS securities, Estimated Fair Value $ 1,625 $ 1,625