Investment Securities, HTM Credit Quality Indicators (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	$ 1,857,150	$ 1,879,005
Not Rated [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	193
US Treasury Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	1,000	999
US Treasury Securities | Not Rated [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0
Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	1,455,462	1,441,900
Obligations of state and political subdivisions (municipal securities) | Not Rated [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	193
FNMA / FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	47,480	54,599
FNMA / FHLMC | Not Rated [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0
GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	87,717	114,553
GNMA | Not Rated [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0
us-Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	63,844	11,211
us-Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial | Not Rated [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0
GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	201,648	255,742
GNMA | Not Rated [Domain]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0
AAA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	984,363	1,004,357
AAA | US Treasury Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	1,000	999
AAA | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	582,675	567,252
AAA | FNMA / FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	47,480	54,599
AAA | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	87,717	114,553
AAA | us-Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	63,844	11,211
AAA | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	201,648	255,742
AA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	860,882	860,607
AA | US Treasury Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
AA | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	860,882	860,607
AA | FNMA / FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
AA | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
AA | us-Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
AA | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
A
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	11,711	14,041
A | US Treasury Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
A | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	11,711	14,041
A | FNMA / FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
A | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
A | us-Federal Home Loan Mortgage Corporation Certificates And Obligations (FHLMC) And Federal National Mortgage Association Certificates And Obligations (FNMA), Commercial
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	0	0
A | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities HTM, net	$ 0	$ 0