Securities (Securities Moody's and Standard & Poor's Bond Rating) (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	$ 3,534,085	$ 3,619,738
States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	2,338,745	2,367,807
States and Political Subdivisions [Member] | Not Guaranteed or Pre-Refunded [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	799,508
States and Political Subdivisions [Member] | Guaranteed by the Texas PSF [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	1,504,951
States and Political Subdivisions [Member] | Guaranteed by Third Party
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	19,755
States and Political Subdivisions [Member] | Pre-Refunded [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	14,531
Other [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	1,500	$ 1,500
Aaa/AAA [Member] | States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	1,834,432
Aaa/AAA [Member] | States and Political Subdivisions [Member] | Not Guaranteed or Pre-Refunded [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	301,310
Aaa/AAA [Member] | States and Political Subdivisions [Member] | Guaranteed by the Texas PSF [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	1,504,951
Aaa/AAA [Member] | States and Political Subdivisions [Member] | Guaranteed by Third Party
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	13,640
Aaa/AAA [Member] | States and Political Subdivisions [Member] | Pre-Refunded [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	14,531
Aaa/AAA [Member] | Other [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Aa/AA [Member] | States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	504,313
Aa/AA [Member] | States and Political Subdivisions [Member] | Not Guaranteed or Pre-Refunded [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	498,198
Aa/AA [Member] | States and Political Subdivisions [Member] | Guaranteed by the Texas PSF [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Aa/AA [Member] | States and Political Subdivisions [Member] | Guaranteed by Third Party
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	6,115
Aa/AA [Member] | States and Political Subdivisions [Member] | Pre-Refunded [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Aa/AA [Member] | Other [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Not rated [Member] | States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Not rated [Member] | States and Political Subdivisions [Member] | Not Guaranteed or Pre-Refunded [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Not rated [Member] | States and Political Subdivisions [Member] | Guaranteed by the Texas PSF [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Not rated [Member] | States and Political Subdivisions [Member] | Guaranteed by Third Party
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Not rated [Member] | States and Political Subdivisions [Member] | Pre-Refunded [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	0
Not rated [Member] | Other [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity, Amortized Cost	$ 1,500