Investment Securities, HTM Credit Quality Indicators (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	$ 2,077,287	$ 2,205,083
US Treasury Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	999	999
Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	1,435,938	$ 1,418,569
FNMA/FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	71,872
GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	207,908
GNMA commercial mortgage-related securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	360,570
AAA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	1,203,018
AAA | US Treasury Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	999
AAA | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	561,670
AAA | FNMA/FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	71,872
AAA | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	207,908
AAA | GNMA commercial mortgage-related securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	360,570
AA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	853,910
AA | US Treasury Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	0
AA | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	853,910
AA | FNMA/FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	0
AA | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	0
AA | GNMA commercial mortgage-related securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	0
A
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	20,358
A | US Treasury Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	0
A | Obligations of state and political subdivisions (municipal securities)
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	20,358
A | FNMA/FHLMC
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	0
A | GNMA
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	0
A | GNMA commercial mortgage-related securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity, net	$ 0