v3.25.2
Securities Securities - Moody's and/or Standard & Poor's Bond Rating (Details) - USD ($)
$ in Thousands
Jun. 30, 2025
Dec. 31, 2024
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity $ 3,486,600 $ 3,534,085
US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 2,324,414 2,338,745
Other Investments [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 1,500 1,500
Moody's, Aaa Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 1,816,877 1,834,432
Moody's, Aaa Rating | Other Investments [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 0 0
Moody's, Aa1 Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 507,537 504,313
Moody's, Aa1 Rating | Other Investments [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 0 0
Not rated [Member] | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 0 0
Not rated [Member] | Other Investments [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 1,500 1,500
Not Guaranteed or Pre-Refunded [Member] | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 794,622 799,508
Not Guaranteed or Pre-Refunded [Member] | Moody's, Aaa Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 300,663 301,310
Not Guaranteed or Pre-Refunded [Member] | Moody's, Aa1 Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 493,959 498,198
Not Guaranteed or Pre-Refunded [Member] | Not rated [Member] | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 0 0
Guaranteed by the Texas PSF [Member] | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 1,495,335 1,504,951
Guaranteed by the Texas PSF [Member] | Moody's, Aaa Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 1,495,335 1,504,951
Guaranteed by the Texas PSF [Member] | Moody's, Aa1 Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 0 0
Guaranteed by the Texas PSF [Member] | Not rated [Member] | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 0 0
Guaranteed by Third Party | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 19,727 19,755
Guaranteed by Third Party | Moody's, Aaa Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 6,149 13,640
Guaranteed by Third Party | Moody's, Aa1 Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 13,578 6,115
Guaranteed by Third Party | Not rated [Member] | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 0 0
Pre-Refunded [Member] | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 14,730 14,531
Pre-Refunded [Member] | Moody's, Aaa Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 14,730 14,531
Pre-Refunded [Member] | Moody's, Aa1 Rating | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity 0 0
Pre-Refunded [Member] | Not rated [Member] | US States and Political Subdivisions Debt Securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Debt Securities, Held-to-maturity $ 0 $ 0