v3.25.2
Securities (Tables)
 6 Months Ended
Jun. 30, 2025
Investments, Debt and Equity Securities [Abstract]  
Debt Securities, Held-to-maturity [Table Text Block] A summary of the amortized cost, fair value and allowance for credit losses related to securities held to maturity as of June 30, 2025 and December 31, 2024, is presented below.
Amortized
Cost		Gross
Unrealized
Gains		Gross
Unrealized
Losses		Estimated
Fair Value		Allowance
for Credit
Losses		Net
Carrying
Amount
June 30, 2025
Residential mortgage-backed securities
$1,160,686 $— $44,267 $1,116,419 $— $1,160,686 
States and political subdivisions
2,324,414 617 224,735 2,100,296 (310)2,324,104 
Other1,500 — 6 1,494 — 1,500 
Total$3,486,600 $617 $269,008 $3,218,209 $(310)$3,486,290 
December 31, 2024
Residential mortgage-backed securities
$1,193,840 $— $71,076 $1,122,764 $— $1,193,840 
States and political subdivisions
2,338,745 13,954 116,414 2,236,285 (310)2,338,435 
Other1,500 — 3 1,497 — 1,500 
Total$3,534,085 $13,954 $187,493 $3,360,546 $(310)$3,533,775 
Moody's and Standard & Poor's Bond Ratings [Table Text Block]
The following table summarizes Moody's and/or Standard & Poor's bond ratings for our portfolio of held-to-maturity securities issued by States and political subdivisions and other securities as of June 30, 2025 and December 31, 2024:
States and Political Subdivisions
Not Guaranteed or Pre-RefundedGuaranteed by the Texas PSFGuaranteed by Third PartyPre-RefundedTotalOther
Securities
June 30, 2025
Aaa/AAA$300,663 $1,495,335 $6,149 $14,730 $1,816,877 $— 
Aa/AA493,959 — 13,578 — 507,537 — 
Not rated— — — — — 1,500 
Total$794,622 $1,495,335 $19,727 $14,730 $2,324,414 $1,500 
December 31, 2024
Aaa/AAA$301,310 $1,504,951 $13,640 $14,531 $1,834,432 $— 
Aa/AA
498,198 — 6,115 — 504,313 — 
Not rated— — — — — 1,500 
Total$799,508 $1,504,951 $19,755 $14,531 $2,338,745 $1,500 
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Table Text Block]
The following table details activity in the allowance for credit losses on held-to-maturity securities during the three and six months ended June 30, 2025 and 2024.
Three Months Ended
June 30,		Six Months Ended
June 30,
2025202420252024
Beginning balance$310 $310 $310 $310 
Credit loss expense (benefit)— — — — 
Ending balance$310 $310 $310 $310 
Amortized Cost, Estimated Fair Value and Allowance for Credit Losses of Securities Available for Sale A summary of the amortized cost, fair value and allowance for credit losses related to securities available for sale as of June 30, 2025 and December 31, 2024, is presented below.
Amortized
Cost		Gross
Unrealized
Gains		Gross
Unrealized
Losses		Allowance
for Credit
Losses		Estimated
Fair Value
June 30, 2025
U.S. Treasury$3,023,961 $— $183,022 $— $2,840,939 
Residential mortgage-backed securities
9,716,684 31,912 898,333 — 8,850,263 
States and political subdivisions
5,246,131 1,631 369,638 — 4,878,124 
Other43,360 — — — 43,360 
Total$18,030,136 $33,543 $1,450,993 $— $16,612,686 
December 31, 2024
U.S. Treasury$3,692,215 $— $249,895 $— $3,442,320 
Residential mortgage-backed securities
8,024,704 2,352 1,029,154 — 6,997,902 
States and political subdivisions
4,842,060 2,493 284,329 — 4,560,224 
Other43,179 — — — 43,179 
Total$16,602,158 $4,845 $1,563,378 $— $15,043,625 
Securities, with Unrealized Losses Segregated by Length of Impairment
The table below summarizes, as of June 30, 2025, securities available for sale in an unrealized loss position for which an allowance for credit losses has not been recorded, aggregated by type of security and length of time in a continuous unrealized loss position.
Less than 12 MonthsMore than 12 MonthsTotal
Estimated
Fair Value		Unrealized
Losses		Estimated
Fair Value		Unrealized
Losses		Estimated
Fair Value		Unrealized
Losses
U.S. Treasury$— $— $2,840,939 $183,022 $2,840,939 $183,022 
Residential mortgage-backed securities1,005,571 7,927 4,627,613 890,406 5,633,184 898,333 
States and political subdivisions1,291,852 55,979 3,224,226 313,659 4,516,078 369,638 
Total$2,297,423 $63,906 $10,692,778 $1,387,087 $12,990,201 $1,450,993 
Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities, Presented by Contractual Maturity The following table summarizes the maturity distribution schedule of securities held to maturity and securities available for sale as of June 30, 2025. Mortgage-backed securities are included in maturity categories based on their stated maturity date. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations. Other securities classified as available for sale include stock in the Federal Reserve Bank and the Federal Home Loan Bank, which have no maturity date. These securities have been included in the total column only.
Within 1 Year1 - 5 Years5 - 10 YearsAfter 10 YearsTotal
Held To Maturity
Amortized Cost
Residential mortgage-backed securities$— $508,570 $11,232 $640,884 $1,160,686 
States and political subdivisions6,445 17,513 69,665 2,230,791 2,324,414 
Other— 1,500 — — 1,500 
Total$6,445 $527,583 $80,897 $2,871,675 $3,486,600 
Estimated Fair Value
Residential mortgage-backed securities$— $473,543 $9,570 $633,306 $1,116,419 
States and political subdivisions6,467 17,709 67,642 2,008,478 2,100,296 
Other— 1,494 — — 1,494 
Total$6,467 $492,746 $77,212 $2,641,784 $3,218,209 
Available For Sale
Amortized Cost
U. S. Treasury$697,559 $1,935,177 $198,253 $192,972 $3,023,961 
Residential mortgage-backed securities— 10,157 2,453 9,704,074 9,716,684 
States and political subdivisions76,817 339,990 757,110 4,072,214 5,246,131 
Other— — — — 43,360 
Total$774,376 $2,285,324 $957,816 $13,969,260 $18,030,136 
Estimated Fair Value
U. S. Treasury$693,221 $1,837,015 $172,984 $137,719 $2,840,939 
Residential mortgage-backed securities— 10,161 2,503 8,837,599 8,850,263 
States and political subdivisions76,787 338,133 722,959 3,740,245 4,878,124 
Other— — — — 43,360 
Total$770,008 $2,185,309 $898,446 $12,715,563 $16,612,686 
Schedule of Realized Gain (Loss) Sales of available for sale securities were as follows:
Three Months Ended
June 30,		Six Months Ended
June 30,
2025202420252024
Proceeds from sales$— $— $38,556 $— 
Gross realized gains— — 43 — 
Gross realized losses— — (57)— 
Tax (expense) benefit of securities gains/losses— — 3 — 
Investment Income Premium amortization and discount accretion included in interest income on securities was as follows:
Three Months Ended
June 30,		Six Months Ended
June 30,
2025202420252024
Premium amortization$(15,078)$(16,570)$(30,091)$(34,523)
Discount accretion4,895 5,032 9,963 9,737 
Net (premium amortization) discount accretion$(10,183)$(11,538)$(20,128)$(24,786)
Trading Account Securities, at Estimated Fair Value Trading account securities, at estimated fair value, were as follows:
June 30,
2025		December 31,
2024
U.S. Treasury$35,515 $33,910 
States and political subdivisions9,775 — 
Total$45,290 $33,910 
Net Gains and Losses on Trading Account Securities
Net gains and losses on trading account securities included in other non-interest income were as follows:
Three Months Ended
June 30,		Six Months Ended
June 30,
2025202420252024
Net gain on sales transactions$1,515 $1,223 $2,788 $2,382 
Net mark-to-market gains (losses)5 (82)(28)(101)
Net gain (loss) on trading account securities$1,520 $1,141 $2,760 $2,281