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SECURITIES AND OTHER INVESTMENTS (Tables) | 6 Months Ended
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Jun. 30, 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
June 30, 2025 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Credit Rating: | ​ |  | ​ | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​
AAA/AA/A | ​ | $ | 719,386 | ​ | $ | — | ​ | $ | 4,311 | ​ | $ | 723,697
BBB/BB/B | ​ | ​ | 1,133 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 1,133
Not Rated – Agency (1) | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 63,430 | ​ | ​ | 63,430
Not Rated – Non-Agency (2) | ​ |  | 9,602 | ​ |  | 2,978 | ​ | ​ | 26,295 | ​ | ​ | 38,875
Total | ​ | $ | 730,121 | ​ | $ | 2,978 | ​ | $ | 94,036 | ​ | $ | 827,135
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 and six months ended June 30, (dollars in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended |  | Six Months Ended
​ | ​ | 2025 | ​ | 2025
Realized gains (losses) (1): |  | ​ |  |  | ​ |
Gross realized gains | ​ | $ | 16 | ​ | $ | 30
Gross realized losses | ​ |  | — | ​ |  | (117)
Net realized gains (losses) | ​ | $ | 16 | ​ | $ | (87)
Proceeds from sales of securities | ​ | $ | 588,546 | ​ | $ | 629,911
​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended |  | Six Months Ended
​ | ​ | 2024 | ​ | 2024
Realized gains (losses) (1): |  | ​ |  |  | ​ |
Gross realized gains | ​ | $ | 9 | ​ | $ | 12
Gross realized losses | ​ |  | (6,525) | ​ |  | (6,525)
Net realized losses | ​ | $ | (6,516) | ​ | $ | (6,513)
Proceeds from sales of securities | ​ | $ | 455,574 | ​ | $ | 517,517
(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 June 30, 2025 are as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Gross Unrealized | ​ | Estimated
​ |  | Cost |  | Gains |  | (Losses) |  | Fair Value
U.S. government and agency securities | ​ | $ | 154,536 | ​ | $ | 712 | ​ | $ | (39) | ​ | $ | 155,209
Obligations of states and political subdivisions | ​ |  | 604,663 | ​ |  | 135 | ​ |  | (137,935) | ​ |  | 466,863
Corporate and other bonds (1) | ​ |  | 268,497 | ​ |  | 512 | ​ |  | (7,774) | ​ |  | 261,235
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ |  | ​
Agency | ​ | ​ | 344,879 | ​ |  | 1,098 | ​ |  | (41,908) | ​ | ​ | 304,069
Non-agency | ​ | ​ | 96,601 | ​ |  | 173 | ​ |  | (2,171) | ​ | ​ | 94,603
Total commercial MBS | ​ | ​ | 441,480 | ​ |  | 1,271 | ​ |  | (44,079) | ​ | ​ | 398,672
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 2,592,111 | ​ |  | 8,133 | ​ |  | (191,707) | ​ | ​ | 2,408,537
Non-agency | ​ | ​ | 118,913 | ​ |  | 809 | ​ |  | (2,866) | ​ | ​ | 116,856
Total residential MBS | ​ | ​ | 2,711,024 | ​ |  | 8,942 | ​ |  | (194,573) | ​ | ​ | 2,525,393
Other securities | ​ |  | 1,909 | ​ |  | — | ​ |  | — | ​ |  | 1,909
Total AFS securities | ​ | $ | 4,182,109 | ​ | $ | 11,572 | ​ | $ | (384,400) | ​ | $ | 3,809,281
(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
June 30, 2025 | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​
U.S. government and agency securities | ​ | $ | 61,143 | ​ | $ | (27) | ​ | $ | 969 | ​ | $ | (12) | ​ | $ | 62,112 | ​ | $ | (39)
Obligations of states and political subdivisions | ​ | ​ | 9,218 | ​ | ​ | (355) | ​ | ​ | 434,111 | ​ | ​ | (137,580) | ​ | ​ | 443,329 | ​ | ​ | (137,935)
Corporate and other bonds (1) | ​ |  | 59,527 | ​ |  | (173) | ​ |  | 127,781 | ​ |  | (7,601) | ​ |  | 187,308 | ​ |  | (7,774)
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 52,923 | ​ | ​ | (185) | ​ | ​ | 159,546 | ​ | ​ | (41,723) | ​ | ​ | 212,469 | ​ | ​ | (41,908)
Non-agency | ​ | ​ | 34,652 | ​ | ​ | (193) | ​ | ​ | 28,613 | ​ | ​ | (1,978) | ​ | ​ | 63,265 | ​ | ​ | (2,171)
Total commercial MBS | ​ | ​ | 87,575 | ​ | ​ | (378) | ​ | ​ | 188,159 | ​ | ​ | (43,701) | ​ | ​ | 275,734 | ​ | ​ | (44,079)
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 407,085 | ​ | ​ | (2,143) | ​ | ​ | 881,959 | ​ | ​ | (189,564) | ​ | ​ | 1,289,044 | ​ | ​ | (191,707)
Non-agency | ​ | ​ | 21,889 | ​ | ​ | (444) | ​ | ​ | 22,089 | ​ | ​ | (2,422) | ​ | ​ | 43,978 | ​ | ​ | (2,866)
Total residential MBS | ​ | ​ | 428,974 | ​ | ​ | (2,587) | ​ | ​ | 904,048 | ​ | ​ | (191,986) | ​ | ​ | 1,333,022 | ​ | ​ | (194,573)
Total AFS securities | ​ | $ | 646,437 | ​ | $ | (3,520) | ​ | $ | 1,655,068 | ​ | $ | (380,880) | ​ | $ | 2,301,505 | ​ | $ | (384,400)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
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 708 and 726 individual securities as of June 30, 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. ​ ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | June 30, 2025 | ​ | December 31, 2024
​ |  | Amortized |  | Estimated |  | Amortized |  | Estimated
​ | ​ | Cost | ​ | Fair Value | ​ | Cost | ​ | Fair Value
Due in one year or less | ​ | $ | 103,377 | ​ | $ | 103,276 | ​ | $ | 35,954 | ​ | $ | 35,808
Due after one year through five years | ​ |  | 276,513 | ​ |  | 276,961 | ​ |  | 215,517 | ​ |  | 215,513
Due after five years through ten years | ​ |  | 545,554 | ​ |  | 527,647 | ​ |  | 286,487 | ​ |  | 271,443
Due after ten years | ​ |  | 3,256,665 | ​ |  | 2,901,397 | ​ |  | 2,306,805 | ​ |  | 1,919,402
Total AFS securities | ​ | $ | 4,182,109 | ​ | $ | 3,809,281 | ​ | $ | 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. ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | June 30, 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 | ​ |  | 18,697 | ​ |  | 19,019 | ​ |  | 18,293 | ​ |  | 18,547
Due after five years through ten years | ​ |  | 166,642 | ​ |  | 158,677 | ​ |  | 115,243 | ​ |  | 109,358
Due after ten years | ​ |  | 641,796 | ​ |  | 600,229 | ​ |  | 666,946 | ​ |  | 628,072
Total HTM securities | ​ | $ | 827,135 | ​ | $ | 777,925 | ​ | $ | 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 | ​ | $ | 730,121 | ​ | $ | 580 | ​ | $ | (38,181) | ​ | $ | 692,520
Corporate and other bonds (1) | ​ | ​ | 2,978 | ​ | ​ | — | ​ | ​ | (47) | ​ | ​ | 2,931
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 26,554 | ​ | ​ | — | ​ | ​ | (5,763) | ​ | ​ | 20,791
Non-agency | ​ | ​ | 15,178 | ​ | ​ | 114 | ​ | ​ | (568) | ​ | ​ | 14,724
Total commercial MBS | ​ | ​ | 41,732 | ​ | ​ | 114 | ​ | ​ | (6,331) | ​ | ​ | 35,515
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 36,876 | ​ | ​ | — | ​ | ​ | (5,152) | ​ | ​ | 31,724
Non-agency | ​ | ​ | 15,428 | ​ | ​ | — | ​ | ​ | (193) | ​ | ​ | 15,235
Total residential MBS | ​ | ​ | 52,304 | ​ | ​ | — | ​ | ​ | (5,345) | ​ | ​ | 46,959
Total HTM securities | ​ | $ | 827,135 | ​ | $ | 694 | ​ | $ | (49,904) | ​ | $ | 777,925
(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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