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
Jun. 30, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities $ 2,798,702 $ 2,439,247
Gross Unrealized Gains 86,241 103,512
Gross Unrealized (Losses) (11,538) (2,340)
Total AFS securities, Estimated Fair Value 2,873,405 2,540,419
U.S. government and agency securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 75,554 13,009
Gross Unrealized Gains 1,099 437
Gross Unrealized (Losses) (44) (52)
Total AFS securities, Estimated Fair Value 76,609 13,394
Obligations of states and political subdivisions    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 899,117 786,466
Gross Unrealized Gains 44,105 50,878
Gross Unrealized (Losses) (751) (18)
Total AFS securities, Estimated Fair Value 942,471 837,326
Corporate and other bonds    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 148,774 148,747
Gross Unrealized Gains 4,156 2,430
Gross Unrealized (Losses) (45) (99)
Total AFS securities, Estimated Fair Value 152,885 151,078
Commercial    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 410,528 372,259
Gross Unrealized Gains 11,719 16,444
Gross Unrealized (Losses) (1,400) (19)
Total AFS securities, Estimated Fair Value 420,847 388,684
Commercial | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 315,274 321,015
Gross Unrealized Gains 11,443 16,277
Gross Unrealized (Losses) (1,119) (2)
Total AFS securities, Estimated Fair Value 325,598 337,290
Commercial | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 95,254 51,244
Gross Unrealized Gains 276 167
Gross Unrealized (Losses) (281) (17)
Total AFS securities, Estimated Fair Value 95,249 51,394
Residential    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,263,097 1,117,141
Gross Unrealized Gains 25,162 33,323
Gross Unrealized (Losses) (9,298) (2,152)
Total AFS securities, Estimated Fair Value 1,278,961 1,148,312
Residential | Agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,190,087 1,012,237
Gross Unrealized Gains 24,025 31,816
Gross Unrealized (Losses) (9,035) (1,946)
Total AFS securities, Estimated Fair Value 1,205,077 1,042,107
Residential | Non-agency    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 73,010 104,904
Gross Unrealized Gains 1,137 1,507
Gross Unrealized (Losses) (263) (206)
Total AFS securities, Estimated Fair Value 73,884 106,205
Other securities    
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Total AFS securities 1,632 1,625
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) 0 0
Total AFS securities, Estimated Fair Value $ 1,632 $ 1,625