Investment Securities, HTM Credit Quality Indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	$ 1,879,005	$ 2,205,083
U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	999	999
Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	1,441,900	$ 1,418,569
FNMA/FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	54,599
GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	114,553
Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	11,211
Government National Mortgage Association Certificates And Obligations (GNMA), Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	255,742
AAA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	1,004,357
AAA | U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	999
AAA | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	567,252
AAA | FNMA/FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	54,599
AAA | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	114,553
AAA | Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	11,211
AAA | Government National Mortgage Association Certificates And Obligations (GNMA), Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	255,742
AA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	860,607
AA | U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
AA | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	860,607
AA | FNMA/FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
AA | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
AA | Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
AA | Government National Mortgage Association Certificates And Obligations (GNMA), Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
A
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	14,041
A | U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
A | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	14,041
A | FNMA/FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
A | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
A | Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	0
A | Government National Mortgage Association Certificates And Obligations (GNMA), Commercial [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	$ 0