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SECURITIES AND OTHER INVESTMENTS (Tables) | 3 Months Ended
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Mar. 31, 2025
Amortized Cost of HTM Securities by Security Type and Credit Rating | The following table presents the amortized cost of HTM securities as of the periods ended, by security type and credit rating (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Obligations of states and political |  | Corporate and other |  | Mortgage-backed |  | Total HTM
​ | ​ | subdivisions | ​ | bonds | ​ | securities | ​ | securities
March 31, 2025 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Credit Rating: | ​ |  | ​ | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​
AAA/AA/A | ​ | $ | 710,141 | ​ | $ | — | ​ | $ | 5,416 | ​ | $ | 715,557
BBB/BB/B | ​ | ​ | 1,139 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 1,139
Not Rated – Agency (1) | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 64,044 | ​ | ​ | 64,044
Not Rated – Non-Agency (2) | ​ |  | 9,608 | ​ |  | 3,087 | ​ | ​ | 27,624 | ​ | ​ | 40,319
Total | ​ | $ | 720,888 | ​ | $ | 3,087 | ​ | $ | 97,084 | ​ | $ | 821,059
December 31, 2024 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Credit Rating: | ​ |  | ​ | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​
AAA/AA/A | ​ | $ | 686,923 | ​ | $ | — | ​ | $ | 5,748 | ​ | $ | 692,671
BBB/BB/B | ​ | ​ | 1,144 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 1,144
Not Rated – Agency (1) | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 64,595 | ​ | ​ | 64,595
Not Rated – Non-Agency (2) | ​ |  | 9,616 | ​ |  | 3,322 | ​ | ​ | 32,503 | ​ | ​ | 45,441
Total | ​ | $ | 697,683 | ​ | $ | 3,322 | ​ | $ | 102,846 | ​ | $ | 803,851
(1) Generally considered not to have credit risk given the government guarantees associated with these agencies. (2) Non-agency mortgage-backed and asset-backed securities have limited credit risk, supported by most receiving a 20% simplified supervisory formula approach rating.
Gross Realized Gain and Losses on the Sale of Securities | The following table presents the gross realized gains and losses on and the proceeds from the sale of securities during the three months ended March 31, (dollars in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2025 |  | 2024
Realized gains (losses): (1) | ​ | ​ | ​ | ​ | ​ | ​
Gross realized gains |  | $ | 14 |  | $ | 3
Gross realized losses | ​ |  | (116) | ​ |  | —
Net realized (losses) gains |  | $ | (102) |  | $ | 3
Proceeds from sales of securities |  | $ | 41,366 |  | $ | 61,943
(1) Includes gains (losses) on sales and calls of securities.
Available-for-sale Securities |
Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities | The amortized cost, gross unrealized gains and losses, and estimated fair values of AFS securities as of March 31, 2025 are as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Gross Unrealized | ​ | Estimated
​ |  | Cost |  | Gains |  | (Losses) |  | Fair Value
U.S. government and agency securities | ​ | $ | 65,428 | ​ | $ | 680 | ​ | $ | (13) | ​ | $ | 66,095
Obligations of states and political subdivisions | ​ |  | 593,973 | ​ |  | 125 | ​ |  | (137,728) | ​ |  | 456,370
Corporate and other bonds (1) | ​ |  | 245,806 | ​ |  | 558 | ​ |  | (7,534) | ​ |  | 238,830
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ |  | ​
Agency | ​ | ​ | 288,399 | ​ |  | 668 | ​ |  | (41,610) | ​ | ​ | 247,457
Non-agency | ​ | ​ | 67,810 | ​ |  | 90 | ​ |  | (1,923) | ​ | ​ | 65,977
Total commercial MBS | ​ | ​ | 356,209 | ​ |  | 758 | ​ |  | (43,533) | ​ | ​ | 313,434
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 1,506,416 | ​ |  | 2,917 | ​ |  | (195,677) | ​ | ​ | 1,313,656
Non-agency | ​ | ​ | 96,155 | ​ |  | 470 | ​ |  | (3,060) | ​ | ​ | 93,565
Total residential MBS | ​ | ​ | 1,602,571 | ​ |  | 3,387 | ​ |  | (198,737) | ​ | ​ | 1,407,221
Other securities | ​ |  | 1,885 | ​ |  | — | ​ |  | — | ​ |  | 1,885
Total AFS securities | ​ | $ | 2,865,872 | ​ | $ | 5,508 | ​ | $ | (387,545) | ​ | $ | 2,483,835
(1) Other bonds include asset-backed securities. The amortized cost, gross unrealized gains and losses, and estimated fair values of AFS securities as of December 31, 2024 are as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Gross Unrealized | ​ | Estimated
​ |  | Cost |  | Gains |  | (Losses) |  | Fair Value
U.S. government and agency securities | ​ | $ | 65,650 | ​ | $ | 390 | ​ | $ | (27) | ​ | $ | 66,013
Obligations of states and political subdivisions | ​ | ​ | 597,956 | ​ |  | 84 | ​ |  | (129,703) | ​ |  | 468,337
Corporate and other bonds (1) | ​ |  | 253,526 | ​ |  | 505 | ​ |  | (9,319) | ​ |  | 244,712
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ |  | ​
Agency | ​ | ​ | 285,949 | ​ |  | 348 | ​ |  | (44,678) | ​ | ​ | 241,619
Non-agency | ​ | ​ | 61,552 | ​ |  | 4 | ​ |  | (2,110) | ​ | ​ | 59,446
Total commercial MBS | ​ | ​ | 347,501 | ​ |  | 352 | ​ |  | (46,788) | ​ | ​ | 301,065
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 1,478,648 | ​ |  | 1,375 | ​ |  | (216,754) | ​ | ​ | 1,263,269
Non-agency | ​ | ​ | 99,622 | ​ |  | 672 | ​ |  | (3,384) | ​ | ​ | 96,910
Total residential MBS | ​ | ​ | 1,578,270 | ​ |  | 2,047 | ​ |  | (220,138) | ​ | ​ | 1,360,179
Other securities | ​ |  | 1,860 | ​ |  | — | ​ |  | — | ​ |  | 1,860
Total AFS securities | ​ | $ | 2,844,763 | ​ | $ | 3,378 | ​ | $ | (405,975) | ​ | $ | 2,442,166
(1) Other bonds include asset-backed securities.
Schedule of Gross Unrealized Losses and Fair Value of Investments | The following table shows the gross unrealized losses and fair value of the Company’s AFS securities with unrealized losses, which are aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position for the following periods ended (dollars in thousands). ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Less than 12 months | ​ | More than 12 months | ​ | Total
​ |  | Fair |  | Unrealized |  | Fair |  | Unrealized |  | Fair |  | Unrealized
​ | ​ | Value | ​ | Losses | ​ | Value(2) | ​ | Losses | ​ | Value | ​ | Losses
March 31, 2025 | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​
U.S. government and agency securities | ​ | $ | — | ​ | $ | — | ​ | $ | 1,094 | ​ | $ | (13) | ​ | $ | 1,094 | ​ | $ | (13)
Obligations of states and political subdivisions | ​ | ​ | 6,008 | ​ | ​ | (377) | ​ | ​ | 434,789 | ​ | ​ | (137,351) | ​ | ​ | 440,797 | ​ | ​ | (137,728)
Corporate and other bonds (1) | ​ |  | 195 | ​ |  | (1) | ​ |  | 152,758 | ​ |  | (7,533) | ​ |  | 152,953 | ​ |  | (7,534)
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 15,166 | ​ | ​ | (83) | ​ | ​ | 161,498 | ​ | ​ | (41,527) | ​ | ​ | 176,664 | ​ | ​ | (41,610)
Non-agency | ​ | ​ | 19,316 | ​ | ​ | (856) | ​ | ​ | 20,262 | ​ | ​ | (1,067) | ​ | ​ | 39,578 | ​ | ​ | (1,923)
Total commercial MBS | ​ | ​ | 34,482 | ​ | ​ | (939) | ​ | ​ | 181,760 | ​ | ​ | (42,594) | ​ | ​ | 216,242 | ​ | ​ | (43,533)
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 108,671 | ​ | ​ | (571) | ​ | ​ | 886,146 | ​ | ​ | (195,106) | ​ | ​ | 994,817 | ​ | ​ | (195,677)
Non-agency | ​ | ​ | 23,135 | ​ | ​ | (197) | ​ | ​ | 26,443 | ​ | ​ | (2,863) | ​ | ​ | 49,578 | ​ | ​ | (3,060)
Total residential MBS | ​ | ​ | 131,806 | ​ | ​ | (768) | ​ | ​ | 912,589 | ​ | ​ | (197,969) | ​ | ​ | 1,044,395 | ​ | ​ | (198,737)
Total AFS securities | ​ | $ | 172,491 | ​ | $ | (2,085) | ​ | $ | 1,682,990 | ​ | $ | (385,460) | ​ | $ | 1,855,481 | ​ | $ | (387,545)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
December 31, 2024 | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |
U.S. government and agency securities | ​ | $ | 1,935 | ​ | $ | (2) | ​ | $ | 1,286 | ​ | $ | (25) | ​ | $ | 3,221 | ​ | $ | (27)
Obligations of states and political subdivisions | ​ | ​ | 6,560 | ​ | ​ | (322) | ​ | ​ | 444,056 | ​ | ​ | (129,381) | ​ | ​ | 450,616 | ​ | ​ | (129,703)
Corporate and other bonds (1) | ​ |  | 8,620 | ​ |  | (27) | ​ |  | 145,655 | ​ |  | (9,292) | ​ |  | 154,275 | ​ |  | (9,319)
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 31,291 | ​ | ​ | (359) | ​ | ​ | 160,880 | ​ | ​ | (44,319) | ​ | ​ | 192,171 | ​ | ​ | (44,678)
Non-agency | ​ | ​ | 24,864 | ​ | ​ | (1,188) | ​ | ​ | 21,110 | ​ | ​ | (922) | ​ | ​ | 45,974 | ​ | ​ | (2,110)
Total commercial MBS | ​ | ​ | 56,155 | ​ | ​ | (1,547) | ​ | ​ | 181,990 | ​ | ​ | (45,241) | ​ | ​ | 238,145 | ​ | ​ | (46,788)
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 104,477 | ​ | ​ | (546) | ​ | ​ | 895,714 | ​ | ​ | (216,208) | ​ | ​ | 1,000,191 | ​ | ​ | (216,754)
Non-agency | ​ | ​ | 6,067 | ​ | ​ | (98) | ​ | ​ | 27,851 | ​ | ​ | (3,286) | ​ | ​ | 33,918 | ​ | ​ | (3,384)
Total residential MBS | ​ | ​ | 110,544 | ​ | ​ | (644) | ​ | ​ | 923,565 | ​ | ​ | (219,494) | ​ | ​ | 1,034,109 | ​ | ​ | (220,138)
Total AFS securities | ​ | $ | 183,814 | ​ | $ | (2,542) | ​ | $ | 1,696,552 | ​ | $ | (403,433) | ​ | $ | 1,880,366 | ​ | $ | (405,975)
(1) Other bonds include asset-backed securities. (2) Comprised of 715 and 726 individual securities as of March 31, 2025 and December 31, 2024, respectively. ​
Schedule of Amortized Cost and Estimated Fair Value of Securities | The following table presents the amortized cost and estimated fair value of AFS securities as of the periods ended, by contractual maturity (dollars in thousands). 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. ​ ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | March 31, 2025 | ​ | December 31, 2024
​ |  | Amortized |  | Estimated |  | Amortized |  | Estimated
​ | ​ | Cost | ​ | Fair Value | ​ | Cost | ​ | Fair Value
Due in one year or less | ​ | $ | 20,877 | ​ | $ | 20,790 | ​ | $ | 35,954 | ​ | $ | 35,808
Due after one year through five years | ​ |  | 225,718 | ​ |  | 226,577 | ​ |  | 215,517 | ​ |  | 215,513
Due after five years through ten years | ​ |  | 288,239 | ​ |  | 270,629 | ​ |  | 286,487 | ​ |  | 271,443
Due after ten years | ​ |  | 2,331,038 | ​ |  | 1,965,839 | ​ |  | 2,306,805 | ​ |  | 1,919,402
Total AFS securities | ​ | $ | 2,865,872 | ​ | $ | 2,483,835 | ​ | $ | 2,844,763 | ​ | $ | 2,442,166
Held-to-maturity Securities |
Schedule of Amortized Cost and Estimated Fair Value of Securities | The following table presents the amortized cost and estimated fair value of HTM securities as of the periods ended, by contractual maturity (dollars in thousands). 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. ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | March 31, 2025 | ​ | December 31, 2024
​ |  | Carrying |  | Estimated |  | Carrying |  | Estimated
​ | ​ | Value | ​ | Fair Value | ​ | Value | ​ | Fair Value
Due in one year or less | ​ | $ | — | ​ | $ | — | ​ | $ | 3,369 | ​ | $ | 3,358
Due after one year through five years | ​ |  | 18,744 | ​ |  | 19,041 | ​ |  | 18,293 | ​ |  | 18,547
Due after five years through ten years | ​ |  | 142,875 | ​ |  | 135,547 | ​ |  | 115,243 | ​ |  | 109,358
Due after ten years | ​ |  | 659,440 | ​ |  | 617,824 | ​ |  | 666,946 | ​ |  | 628,072
Total HTM securities | ​ | $ | 821,059 | ​ | $ | 772,412 | ​ | $ | 803,851 | ​ | $ | 759,335
Schedule of Carrying Values, Gross Unrealized Gains and Losses and Estimated Fair Value of Securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Carrying | ​ | Gross Unrealized | ​ | Estimated
​ |  | Value |  | Gains |  | (Losses) | ​ | Fair Value
Obligations of states and political subdivisions | ​ | $ | 720,888 | ​ | $ | 665 | ​ | $ | (37,312) | ​ | $ | 684,241
Corporate and other bonds (1) | ​ | ​ | 3,087 | ​ | ​ | — | ​ | ​ | (59) | ​ | ​ | 3,028
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 26,671 | ​ | ​ | — | ​ | ​ | (5,780) | ​ | ​ | 20,891
Non-agency | ​ | ​ | 16,824 | ​ | ​ | 102 | ​ | ​ | (585) | ​ | ​ | 16,341
Total commercial MBS | ​ | ​ | 43,495 | ​ | ​ | 102 | ​ | ​ | (6,365) | ​ | ​ | 37,232
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 37,373 | ​ | ​ | — | ​ | ​ | (5,450) | ​ | ​ | 31,923
Non-agency | ​ | ​ | 16,216 | ​ | ​ | — | ​ | ​ | (228) | ​ | ​ | 15,988
Total residential MBS | ​ | ​ | 53,589 | ​ | ​ | — | ​ | ​ | (5,678) | ​ | ​ | 47,911
Total HTM securities | ​ | $ | 821,059 | ​ | $ | 767 | ​ | $ | (49,414) | ​ | $ | 772,412
(1) Other bonds include asset-backed securities. ​ ​ The carrying value, gross unrealized gains and losses, and estimated fair values of HTM securities as of December 31, 2024 are as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Carrying | ​ | Gross Unrealized | ​ | Estimated
​ |  | Value |  | Gains |  | (Losses) |  | Fair Value
Obligations of states and political subdivisions | ​ | $ | 697,683 | ​ | $ | 715 | ​ | $ | (31,763) | ​ | $ | 666,635
Corporate and other bonds (1) | ​ | ​ | 3,322 | ​ | ​ | — | ​ | ​ | (82) | ​ | ​ | 3,240
Commercial MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 26,787 | ​ | ​ | — | ​ | ​ | (6,185) | ​ | ​ | 20,602
Non-agency | ​ | ​ | 17,922 | ​ | ​ | 28 | ​ | ​ | (659) | ​ | ​ | 17,291
Total commercial MBS | ​ | ​ | 44,709 | ​ | ​ | 28 | ​ | ​ | (6,844) | ​ | ​ | 37,893
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 37,808 | ​ | ​ | — | ​ | ​ | (6,288) | ​ | ​ | 31,520
Non-agency | ​ | ​ | 20,329 | ​ | ​ | — | ​ | ​ | (282) | ​ | ​ | 20,047
Total residential MBS | ​ | ​ | 58,137 | ​ | ​ | — | ​ | ​ | (6,570) | ​ | ​ | 51,567
Total HTM securities | ​ | $ | 803,851 | ​ | $ | 743 | ​ | $ | (45,259) | ​ | $ | 759,335
(1) Other bonds include asset-backed securities.

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