| Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] |
Investment Securities Investment securities are designated as AFS, HTM, or equity on the consolidated balance sheets. The amortized cost and fair values of AFS and HTM securities at September 30, 2026 were as follows: | | | | | | | | | | | | | | | | (in thousands) | Amortized
Cost | Gross
Unrealized
Gains | Gross
Unrealized
Losses | Fair Value | | | | AFS investment securities | | | | | | | | | | | | | | | | Obligations of state and political subdivisions (municipal securities) | $ | 6,849 | | $ | — | | $ | (457) | | $ | 6,392 | | | Residential mortgage-related securities: | | | | | | FNMA/FHLMC | 146,337 | | 106 | | (11,979) | | 134,464 | | | GNMA | 5,542,393 | | 317 | | (190,604) | | 5,352,106 | | | | | | | | Commercial mortgage-related securities: | | | | | | FNMA/FHLMC | 369,363 | | — | | (21,964) | | 347,399 | | | GNMA | 111,099 | | — | | (8,236) | | 102,863 | | | Asset backed securities: | | | | | | FFELP | 86,587 | | 34 | | (573) | | 86,048 | | | SBA | 174,150 | | — | | (9,648) | | 164,502 | | | | | | | Other debt securities(a) | 6,750 | | — | | (1,696) | | 5,054 | | | Total AFS investment securities | $ | 6,443,528 | | $ | 457 | | $ | (245,157) | | $ | 6,198,828 | | | HTM investment securities | | | | | | U.S. Treasury securities | $ | 997 | | $ | — | | $ | (4) | | $ | 993 | | | Obligations of state and political subdivisions (municipal securities) | 1,576,827 | | 44 | | (272,110) | | 1,304,761 | | | Residential mortgage-related securities: | | | | | | FNMA/FHLMC | 771,047 | | — | | (172,347) | | 598,700 | | | GNMA | 36,181 | | — | | (4,547) | | 31,634 | | | Private-label | 284,928 | | — | | (60,012) | | 224,916 | | | Commercial mortgage-related securities: | | | | | | FNMA/FHLMC | 752,924 | | — | | (143,020) | | 609,904 | | | GNMA | 39,316 | | — | | (5,342) | | 33,974 | | | Total HTM investment securities | $ | 3,462,220 | | $ | 44 | | $ | (657,382) | | $ | 2,804,882 | | | | | | |
(a)Unrealized losses includes allowance for credit losses The amortized cost and fair values of AFS and HTM securities at December 31, 2025 were as follows: | | | | | | | | | | | | | | | | (in thousands) | Amortized
Cost | Gross
Unrealized
Gains | Gross
Unrealized
Losses | Fair Value | | | | AFS investment securities | | | | | | | | | | | | | | | | Obligations of state and political subdivisions (municipal securities) | $ | 3,063 | | $ | 1 | | $ | (20) | | $ | 3,044 | | | Residential mortgage-related securities: | | | | | | FNMA/FHLMC | 134,142 | | 1,214 | | (5,493) | | 129,863 | | | GNMA | 5,000,015 | | 40,067 | | (253) | | 5,039,829 | | | | | | | | Commercial mortgage-related securities: | | | | | | FNMA/FHLMC | 17,959 | | — | | (1,001) | | 16,958 | | | GNMA | 113,374 | | — | | (3,818) | | 109,556 | | | Asset backed securities: | | | | | | FFELP | 95,977 | | 19 | | (950) | | 95,046 | | | SBA | 283 | | — | | (14) | | 269 | | | | | | | | Other debt securities | 3,000 | | — | | (2) | | 2,998 | | | Total AFS investment securities | $ | 5,367,813 | | $ | 41,301 | | $ | (11,551) | | $ | 5,397,563 | | | HTM investment securities | | | | | | U.S. Treasury securities | $ | 996 | | $ | 19 | | $ | — | | $ | 1,015 | | | Obligations of state and political subdivisions (municipal securities) | 1,628,088 | | 3,070 | | (123,856) | | 1,507,302 | | | Residential mortgage-related securities: | | | | | | FNMA/FHLMC | 823,630 | | 165 | | (127,333) | | 696,462 | | | GNMA | 39,123 | | 82 | | (2,321) | | 36,884 | | | Private-label | 302,817 | | — | | (43,990) | | 258,827 | | | Commercial mortgage-related securities: | | | | | | FNMA/FHLMC | 763,370 | | — | | (113,004) | | 650,366 | | | GNMA | 44,552 | | 152 | | (4,566) | | 40,138 | | | Total HTM investment securities | $ | 3,602,576 | | $ | 3,488 | | $ | (415,070) | | $ | 3,190,994 | | | | | | | | | | | |
Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. The expected maturities of AFS and HTM securities at September 30, 2026, are shown below: | | | | | | | | | | | | | | | | AFS | HTM | | (in thousands) | Amortized
Cost | Fair
Value | Amortized
Cost | Fair
Value | | Due in one year or less | $ | 4,750 | | $ | 3,059 | | $ | 7,118 | | $ | 7,080 | | | Due after one year through five years | 6,243 | | 6,002 | | 90,248 | | 87,290 | | | Due after five years through ten years | — | | — | | 333,317 | | 302,799 | | | Due after ten years | 2,606 | | 2,385 | | 1,147,141 | | 908,585 | | | Total municipal, U.S. Treasury and other debt securities | 13,599 | | 11,446 | | 1,577,824 | | 1,305,754 | | | Residential mortgage-related securities: | | | | | | FNMA/FHLMC | 146,337 | | 134,464 | | 771,047 | | 598,700 | | | GNMA | 5,542,393 | | 5,352,106 | | 36,181 | | 31,634 | | | Private-label | — | | — | | 284,928 | | 224,916 | | | Commercial mortgage-related securities: | | | | | | FNMA/FHLMC | 369,363 | | 347,399 | | 752,924 | | 609,904 | | | GNMA | 111,099 | | 102,863 | | 39,316 | | 33,974 | | | Asset backed securities: | | | | | | FFELP | 86,587 | | 86,048 | | — | | — | | | SBA | 174,150 | | 164,502 | | — | | — | | | | | | | | Total investment securities | $ | 6,443,528 | | $ | 6,198,828 | | $ | 3,462,220 | | $ | 2,804,882 | | | Ratio of fair value to amortized cost | | 96.2 | % | | 81.0 | % |
Investment securities with a carrying value of $1.0 billion at September 30, 2026 and $1.2 billion at December 31, 2025, respectively, were pledged as required to secure certain deposits or for other purposes. Accrued interest receivable on HTM securities totaled $14.6 million and $17.7 million at September 30, 2026 and December 31, 2025, respectively. Accrued interest receivable on AFS securities totaled $25.0 million and $23.0 million at September 30, 2026 and December 31, 2025, respectively. Accrued interest receivable on both HTM and AFS securities is included in interest receivable on the consolidated balance sheets. The Corporation holds U.S. Treasury, municipal, and mortgage-related securities issued by the U.S. government or a GSE which are backed by the full faith and credit of the U.S. government or are GSE guaranteed. The Corporation also holds private-label residential mortgage-related securities that have credit enhancement which covers the first 16% of losses and, as a result, no allowance for credit losses has been recorded related to these securities. There was a $0.1 million allowance for credit losses on HTM securities at September 30, 2026 and $0.1 million at December 31, 2025, attributable entirely to the Corporation's municipal securities, included in HTM investment securities, net, at amortized cost on the consolidated balance sheets. The allowance for credit losses on AFS securities was $1.7 million at September 30, 2026 and zero at December 31, 2025, attributable to a corporate bond acquired through the recent acquisition of American National, included in other debt securities within the AFS investment securities, net, caption on the consolidated balance sheets.
The following represents gross unrealized losses and the related fair value of AFS and HTM securities, aggregated by investment category and length of time individual securities have been in a continuous unrealized loss position, at September 30, 2026: | | | | | | | | | | | | | | | | | | | | | | | | | | | | Less than 12 months | 12 months or more | Total | | (in thousands) | Number
of
Securities | Unrealized
Losses | Fair
Value | Number
of
Securities | Unrealized
Losses | Fair
Value | Unrealized
Losses | Fair
Value | | AFS investment securities | | | | | | | | | | | | | | | | | | | | | | | | | | | | Obligations of state and political subdivisions (municipal securities) | 8 | | $ | (441) | | $ | 6,158 | | 1 | | $ | (16) | | $ | 234 | | $ | (457) | | $ | 6,392 | | | Residential mortgage-related securities: | | | | | | | | | | FNMA/FHLMC | 62 | | (4,607) | | 84,740 | | 8 | | (7,372) | | 44,429 | | (11,979) | | 129,169 | | | GNMA | 384 | | (190,401) | | 5,247,698 | | 3 | | (203) | | 2,669 | | (190,604) | | 5,250,367 | | | | | | | | | | | | Commercial mortgage-related securities: | | | | | | | | | | FNMA/FHLMC | 9 | | (20,066) | | 331,626 | | 1 | | (1,898) | | 15,773 | | (21,964) | | 347,399 | | | GNMA | — | | — | | — | | 15 | | (8,236) | | 102,864 | | (8,236) | | 102,864 | | | Asset backed securities: | | | | | | | | | | FFELP | 1 | | (34) | | 5,618 | | 12 | | (539) | | 50,269 | | (573) | | 55,887 | | | SBA | 9 | | (9,641) | | 164,402 | | 2 | | (7) | | 99 | | (9,648) | | 164,501 | | Other debt securities(a) | 3 | | (1,696) | | 4,054 | | — | | — | | — | | (1,696) | | 4,054 | | | | | | | | | | | | Total | 476 | | $ | (226,886) | | $ | 5,844,296 | | 42 | | $ | (18,271) | | $ | 216,337 | | $ | (245,157) | | $ | 6,060,633 | | | HTM investment securities | | | | | | | | | | U.S. Treasury securities | 1 | | $ | (4) | | $ | 994 | | — | | $ | — | | $ | — | | $ | (4) | | $ | 994 | | | Obligations of state and political subdivisions (municipal securities) | 636 | | $ | (68,956) | | $ | 755,193 | | 408 | | $ | (203,154) | | $ | 539,761 | | $ | (272,110) | | $ | 1,294,954 | | | Residential mortgage-related securities: | | | | | | | | | | FNMA/FHLMC | 21 | | (1,262) | | 20,955 | | 99 | | (171,085) | | 577,745 | | (172,347) | | 598,700 | | | GNMA | 7 | | (555) | | 7,473 | | 78 | | (3,992) | | 24,161 | | (4,547) | | 31,634 | | | Private-label | — | | — | | — | | 18 | | (60,012) | | 224,916 | | (60,012) | | 224,916 | | | Commercial mortgage-related securities: | | | | | | | | | | FNMA/FHLMC | 2 | | (1,985) | | 24,674 | | 43 | | (141,035) | | 585,230 | | (143,020) | | 609,904 | | | GNMA | — | | — | | — | | 13 | | (5,342) | | 33,974 | | (5,342) | | 33,974 | | | Total | 667 | | $ | (72,762) | | $ | 809,289 | | 659 | | $ | (584,620) | | $ | 1,985,787 | | $ | (657,382) | | $ | 2,795,076 | |
(a)Unrealized losses includes allowance for credit losses For comparative purposes, the following represents gross unrealized losses and the related fair value of AFS and HTM securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2025: | | | | | | | | | | | | | | | | | | | | | | | | | | | | Less than 12 months | 12 months or more | Total | | (in thousands) | Number
of
Securities | Unrealized
Losses | Fair
Value | Number
of
Securities | Unrealized
Losses | Fair
Value | Unrealized
Losses | Fair
Value | | AFS investment securities | | | | | | | | | | | | | | | | | | | | | | | | | | | | Obligations of state and political subdivisions (municipal securities) | — | | $ | — | | $ | — | | 2 | | $ | (20) | | $ | 863 | | $ | (20) | | $ | 863 | | | Residential mortgage-related securities: | | | | | | | | | | FNMA/FHLMC | 12 | | (95) | | 14,155 | | 12 | | (5,398) | | 56,215 | | (5,493) | | 70,370 | | | GNMA | 16 | | (232) | | 143,734 | | 3 | | (21) | | 2,674 | | (253) | | 146,408 | | | | | | | | | | | | Commercial mortgage-related securities: | | | | | | | | | | FNMA/FHLMC | — | | — | | — | | 1 | | (1,001) | | 16,958 | | (1,001) | | 16,958 | | | GNMA | — | | — | | — | | 15 | | (3,818) | | 109,556 | | (3,818) | | 109,556 | | | Asset backed securities: | | | | | | | | | | FFELP | 2 | | (152) | | 33,239 | | 12 | | (798) | | 55,565 | | (950) | | 88,804 | | | SBA | — | | — | | — | | 2 | | (14) | | 231 | | (14) | | 231 | | | Other debt securities | 2 | | (2) | | 1,998 | | — | | — | | — | | (2) | | 1,998 | | | | | | | | | | | | Total | 32 | | $ | (481) | | $ | 193,126 | | 47 | | $ | (11,070) | | $ | 242,062 | | $ | (11,551) | | $ | 435,188 | | | HTM investment securities | | | | | | | | | | | | | | | | | | | Obligations of state and political subdivisions (municipal securities) | 81 | | $ | (2,978) | | $ | 89,826 | | 543 | | $ | (120,878) | | $ | 842,485 | | $ | (123,856) | | $ | 932,311 | | | Residential mortgage-related securities: | | | | | | | | | | FNMA/FHLMC | 1 | | — | | 30 | | 102 | | (127,333) | | 676,915 | | (127,333) | | 676,945 | | | GNMA | — | | — | | — | | 80 | | (2,321) | | 30,237 | | (2,321) | | 30,237 | | | Private-label | — | | — | | — | | 18 | | (43,990) | | 258,827 | | (43,990) | | 258,827 | | | Commercial mortgage-related securities: | | | | | | | | | | FNMA/FHLMC | 2 | | (470) | | 26,287 | | 43 | | (112,534) | | 624,079 | | (113,004) | | 650,366 | | | GNMA | — | | — | | — | | 13 | | (4,566) | | 40,138 | | (4,566) | | 40,138 | | | Total | 84 | | $ | (3,448) | | $ | 116,143 | | 799 | | $ | (411,622) | | $ | 2,472,681 | | $ | (415,070) | | $ | 2,588,824 | |
On a quarterly basis, the Corporation refreshes the credit quality of each HTM security. The Company monitors the credit quality of HTM securities through credit ratings provided by S&P and Moody’s. Investment grade securities are rated BBB- or higher by S&P, or Baa3 or higher by Moody’s, and are generally considered by the rating agencies and market participants to be of low credit risk. As of September 30, 2026 and December 31, 2025, the Corporation's HTM portfolio contained all investment grade securities except for securities that were not rated which were individually reviewed noting no credit quality issues. Based on the Corporation’s evaluation, management does not believe any unrealized losses at September 30, 2026 represent credit deterioration as these unrealized losses are primarily attributable to changes in interest rates and the current market conditions, except as disclosed above. As of September 30, 2026, the Corporation does not intend to sell, nor does it believe that it will be required to sell, the securities in an unrealized loss position before recovery of their amortized cost basis. Regulatory stocks: The Corporation had FHLB stock of $188.4 million and $154.4 million at September 30, 2026 and December 31, 2025, respectively. The Corporation had Federal Reserve Bank stock of $115.9 million and $98.1 million at September 30, 2026 and December 31, 2025, respectively. Accrued interest receivable on FHLB stock totaled $4.1 million at September 30, 2026 and $2.8 million at December 31, 2025. There was $1.7 million accrued interest receivable on Federal Reserve Bank Stock at September 30, 2026 and none at December 31, 2025. Accrued interest receivable on both FHLB stock and Federal Reserve Bank stock is included in interest receivable on the consolidated balance sheets. Equity Securities Equity securities with readily determinable fair values: The Corporation's portfolio of equity securities with readily determinable fair values is primarily comprised of mutual funds. The Corporation had equity securities with readily determinable fair values of $15.0 million and $11.1 million at September 30, 2026 and December 31, 2025, respectively. Equity securities without readily determinable fair values: The Corporation's portfolio of equity securities without readily determinable fair values primarily consists of an investment in a private loan fund. The Corporation had equity securities without readily determinable fair values carried at $15.0 million at both September 30, 2026 and December 31, 2025.
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