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, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities $ 3,150,256 $ 2,439,247
Gross Unrealized Gains 70,084 103,512
Gross Unrealized (Losses) (25,164) (2,340)
Total AFS securities, Estimated Fair Value 3,195,176 2,540,419
U.S. government and agency securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 74,214 13,009
Gross Unrealized Gains 645 437
Gross Unrealized (Losses) (41) (52)
Total AFS securities, Estimated Fair Value 74,818 13,394
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 971,987 786,466
Gross Unrealized Gains 34,885 50,878
Gross Unrealized (Losses) (7,991) (18)
Total AFS securities, Estimated Fair Value 998,881 837,326
Corporate and other bonds    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 145,151 148,747
Gross Unrealized Gains 3,931 2,430
Gross Unrealized (Losses) (54) (99)
Total AFS securities, Estimated Fair Value 149,028 151,078
Commercial    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 433,732 372,259
Gross Unrealized Gains 9,463 16,444
Gross Unrealized (Losses) (2,853) (19)
Total AFS securities, Estimated Fair Value 440,342 388,684
Commercial | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 338,327 321,015
Gross Unrealized Gains 9,213 16,277
Gross Unrealized (Losses) (2,557) (2)
Total AFS securities, Estimated Fair Value 344,983 337,290
Commercial | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 95,405 51,244
Gross Unrealized Gains 250 167
Gross Unrealized (Losses) (296) (17)
Total AFS securities, Estimated Fair Value 95,359 51,394
Residential    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,523,536 1,117,141
Gross Unrealized Gains 21,160 33,323
Gross Unrealized (Losses) (14,225) (2,152)
Total AFS securities, Estimated Fair Value 1,530,471 1,148,312
Residential | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,449,753 1,012,237
Gross Unrealized Gains 20,630 31,816
Gross Unrealized (Losses) (14,030) (1,946)
Total AFS securities, Estimated Fair Value 1,456,353 1,042,107
Residential | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 73,783 104,904
Gross Unrealized Gains 530 1,507
Gross Unrealized (Losses) (195) (206)
Total AFS securities, Estimated Fair Value 74,118 106,205
Other securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,636 1,625
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Total AFS securities, Estimated Fair Value $ 1,636 $ 1,625