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SECURITIES AND OTHER INVESTMENTS (Tables) | 9 Months Ended
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Sep. 30, 2024
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
September 30, 2024 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Credit Rating: | ​ |  | ​ | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​
AAA/AA/A | ​ | $ | 684,805 | ​ | $ | — | ​ | $ | 6,439 | ​ | $ | 691,244
BBB/BB/B | ​ | ​ | 1,150 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 1,150
Not Rated – Agency(1) | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 67,416 | ​ | ​ | 67,416
Not Rated – Non-Agency(2) | ​ |  | 9,505 | ​ |  | 3,484 | ​ | ​ | 34,281 | ​ | ​ | 47,270
Total | ​ | $ | 695,460 | ​ | $ | 3,484 | ​ | $ | 108,136 | ​ | $ | 807,080
December 31, 2023 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Credit Rating: | ​ |  | ​ | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​
AAA/AA/A | ​ | $ | 688,499 | ​ | $ | — | ​ | $ | 9,720 | ​ | $ | 698,219
BBB/BB/B | ​ | ​ | 1,166 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 1,166
Not Rated – Agency(1) | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 68,039 | ​ | ​ | 68,039
Not Rated – Non-Agency(2) | ​ |  | 9,524 | ​ |  | 4,349 | ​ | ​ | 56,081 | ​ | ​ | 69,954
Total | ​ | $ | 699,189 | ​ | $ | 4,349 | ​ | $ | 133,840 | ​ | $ | 837,378
(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 nine months ended September 30, (dollars in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended |  | Nine Months Ended
​ | ​ | 2024 | ​ | 2024
Realized gains (losses)(1): |  | ​ |  |  | ​ |
Gross realized gains | ​ | $ | 4 | ​ | $ | 16
Gross realized losses | ​ |  | — | ​ |  | (6,526)
Net realized gains (losses) | ​ | $ | 4 | ​ | $ | (6,510)
​ | ​ | ​ | ​ | ​ | ​ | ​
Proceeds from sales of securities | ​ | $ | 102,888 | ​ | $ | 620,405
​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended |  | Nine Months Ended
​ | ​ | 2023 | ​ | 2023
Realized gains (losses)(1): |  | ​ |  |  | ​ |
Gross realized gains | ​ | $ | 4 | ​ | $ | 1,352
Gross realized losses | ​ |  | (27,598) | ​ |  | (42,344)
Net realized losses | ​ | $ | (27,594) | ​ | $ | (40,992)
​ | ​ | ​ | ​ | ​ | ​ | ​
Proceeds from sales of securities | ​ | $ | 256,780 | ​ | $ | 856,881
(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 September 30, 2024 are as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Gross Unrealized | ​ | Estimated
​ |  | Cost |  | Gains |  | (Losses) |  | Fair Value
September 30, 2024 |  | ​ |  |  | ​ |  |  | ​ |  | ​ | ​ |
U.S. government and agency securities | ​ | $ | 65,384 | ​ | $ | 1,313 | ​ | $ | (26) | ​ | $ | 66,671
Obligations of states and political subdivisions | ​ |  | 600,074 | ​ |  | 294 | ​ |  | (111,841) | ​ |  | 488,527
Corporate and other bonds (1) | ​ |  | 283,861 | ​ |  | 631 | ​ |  | (12,517) | ​ |  | 271,975
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ |  | ​
Agency | ​ | ​ | 287,747 | ​ |  | 1,724 | ​ |  | (37,721) | ​ | ​ | 251,750
Non-agency | ​ | ​ | 76,501 | ​ |  | 202 | ​ |  | (1,636) | ​ | ​ | 75,067
Total commercial MBS | ​ | ​ | 364,248 | ​ |  | 1,926 | ​ |  | (39,357) | ​ | ​ | 326,817
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 1,522,319 | ​ |  | 4,144 | ​ |  | (176,187) | ​ | ​ | 1,350,276
Non-agency | ​ | ​ | 104,967 | ​ |  | 984 | ​ |  | (3,867) | ​ | ​ | 102,084
Total residential MBS | ​ | ​ | 1,627,286 | ​ |  | 5,128 | ​ |  | (180,054) | ​ | ​ | 1,452,360
Other securities | ​ |  | 1,832 | ​ |  | — | ​ |  | — | ​ |  | 1,832
Total AFS securities | ​ | $ | 2,942,685 | ​ | $ | 9,292 | ​ | $ | (343,795) | ​ | $ | 2,608,182
(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, 2023 are as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | Gross Unrealized | ​ | Estimated
​ |  | Cost |  | Gains |  | (Losses) |  | Fair Value
December 31, 2023 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government and agency securities | ​ | $ | 62,367 | ​ | $ | 1,023 | ​ | $ | (34) | ​ | $ | 63,356
Obligations of states and political subdivisions | ​ | ​ | 586,865 | ​ |  | 33 | ​ |  | (111,451) | ​ |  | 475,447
Corporate and other bonds (1) | ​ |  | 261,656 | ​ |  | 7 | ​ |  | (19,774) | ​ |  | 241,889
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ |  | ​
Agency | ​ | ​ | 233,775 | ​ |  | 274 | ​ |  | (41,181) | ​ | ​ | 192,868
Non-agency | ​ | ​ | 66,743 | ​ |  | — | ​ |  | (1,965) | ​ | ​ | 64,778
Total commercial MBS | ​ | ​ | 300,518 | ​ |  | 274 | ​ |  | (43,146) | ​ | ​ | 257,646
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 1,312,538 | ​ |  | 114 | ​ |  | (205,635) | ​ | ​ | 1,107,017
Non-agency | ​ | ​ | 89,840 | ​ |  | 141 | ​ |  | (5,827) | ​ | ​ | 84,154
Total residential MBS | ​ | ​ | 1,402,378 | ​ |  | 255 | ​ |  | (211,462) | ​ | ​ | 1,191,171
Other securities | ​ |  | 1,752 | ​ |  | — | ​ |  | — | ​ |  | 1,752
Total AFS securities | ​ | $ | 2,615,536 | ​ | $ | 1,592 | ​ | $ | (385,867) | ​ | $ | 2,231,261
(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
September 30, 2024 | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​
U.S. government and agency securities | ​ | $ | — | ​ | $ | — | ​ | $ | 1,439 | ​ | $ | (26) | ​ | $ | 1,439 | ​ | $ | (26)
Obligations of states and political subdivisions | ​ | ​ | 1,277 | ​ | ​ | (213) | ​ | ​ | 462,306 | ​ | ​ | (111,628) | ​ | ​ | 463,583 | ​ | ​ | (111,841)
Corporate and other bonds(1) | ​ |  | 14,899 | ​ |  | (167) | ​ |  | 188,773 | ​ |  | (12,350) | ​ |  | 203,672 | ​ |  | (12,517)
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 25,224 | ​ | ​ | (86) | ​ | ​ | 148,257 | ​ | ​ | (37,635) | ​ | ​ | 173,481 | ​ | ​ | (37,721)
Non-agency | ​ | ​ | 17,533 | ​ | ​ | (616) | ​ | ​ | 40,135 | ​ | ​ | (1,020) | ​ | ​ | 57,668 | ​ | ​ | (1,636)
Total commercial MBS | ​ | ​ | 42,757 | ​ | ​ | (702) | ​ | ​ | 188,392 | ​ | ​ | (38,655) | ​ | ​ | 231,149 | ​ | ​ | (39,357)
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 94,214 | ​ | ​ | (288) | ​ | ​ | 947,499 | ​ | ​ | (175,899) | ​ | ​ | 1,041,713 | ​ | ​ | (176,187)
Non-agency | ​ | ​ | 16,199 | ​ | ​ | (96) | ​ | ​ | 29,821 | ​ | ​ | (3,771) | ​ | ​ | 46,020 | ​ | ​ | (3,867)
Total residential MBS | ​ | ​ | 110,413 | ​ | ​ | (384) | ​ | ​ | 977,320 | ​ | ​ | (179,670) | ​ | ​ | 1,087,733 | ​ | ​ | (180,054)
Total AFS securities | ​ | $ | 169,346 | ​ | $ | (1,466) | ​ | $ | 1,818,230 | ​ | $ | (342,329) | ​ | $ | 1,987,576 | ​ | $ | (343,795)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
December 31, 2023 | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |
U.S. government and agency securities | ​ | $ | — | ​ | $ | — | ​ | $ | 1,980 | ​ | $ | (34) | ​ | $ | 1,980 | ​ | $ | (34)
Obligations of states and political subdivisions | ​ | ​ | 11,758 | ​ | ​ | (2,090) | ​ | ​ | 455,931 | ​ | ​ | (109,361) | ​ | ​ | 467,689 | ​ | ​ | (111,451)
Corporate and other bonds(1) | ​ |  | 89,450 | ​ |  | (531) | ​ |  | 144,155 | ​ |  | (19,243) | ​ |  | 233,605 | ​ |  | (19,774)
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 35,665 | ​ | ​ | (547) | ​ | ​ | 143,657 | ​ | ​ | (40,634) | ​ | ​ | 179,322 | ​ | ​ | (41,181)
Non-agency | ​ | ​ | — | ​ | ​ | — | ​ | ​ | 64,778 | ​ | ​ | (1,965) | ​ | ​ | 64,778 | ​ | ​ | (1,965)
Total commercial MBS | ​ | ​ | 35,665 | ​ | ​ | (547) | ​ | ​ | 208,435 | ​ | ​ | (42,599) | ​ | ​ | 244,100 | ​ | ​ | (43,146)
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 59,707 | ​ | ​ | (491) | ​ | ​ | 1,011,809 | ​ | ​ | (205,144) | ​ | ​ | 1,071,516 | ​ | ​ | (205,635)
Non-agency | ​ | ​ | 9,022 | ​ | ​ | (41) | ​ | ​ | 40,085 | ​ | ​ | (5,786) | ​ | ​ | 49,107 | ​ | ​ | (5,827)
Total residential MBS | ​ | ​ | 68,729 | ​ | ​ | (532) | ​ | ​ | 1,051,894 | ​ | ​ | (210,930) | ​ | ​ | 1,120,623 | ​ | ​ | (211,462)
Total AFS securities | ​ | $ | 205,602 | ​ | $ | (3,700) | ​ | $ | 1,862,395 | ​ | $ | (382,167) | ​ | $ | 2,067,997 | ​ | $ | (385,867)
(1) Other bonds include asset-backed securities. (2) Comprised of 740 and 757 individual securities as of September 30, 2024 and December 31, 2023, 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. ​ ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2024 | ​ | December 31, 2023
​ |  | Amortized |  | Estimated |  | Amortized |  | Estimated
​ | ​ | Cost | ​ | Fair Value | ​ | Cost | ​ | Fair Value
Due in one year or less | ​ | $ | 49,287 | ​ | $ | 49,040 | ​ | $ | 52,427 | ​ | $ | 51,936
Due after one year through five years | ​ |  | 214,039 | ​ |  | 215,657 | ​ |  | 150,271 | ​ |  | 149,545
Due after five years through ten years | ​ |  | 322,155 | ​ |  | 305,664 | ​ |  | 282,309 | ​ |  | 261,720
Due after ten years | ​ |  | 2,357,204 | ​ |  | 2,037,821 | ​ |  | 2,130,529 | ​ |  | 1,768,060
Total AFS securities | ​ | $ | 2,942,685 | ​ | $ | 2,608,182 | ​ | $ | 2,615,536 | ​ | $ | 2,231,261
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. ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2024 | ​ | December 31, 2023
​ |  | Carrying |  | Estimated |  | Carrying |  | Estimated
​ | ​ | Value | ​ | Fair Value | ​ | Value | ​ | Fair Value
Due in one year or less | ​ | $ | 4,022 | ​ | $ | 3,997 | ​ | $ | 3,065 | ​ | $ | 3,058
Due after one year through five years | ​ |  | 13,173 | ​ |  | 13,554 | ​ |  | 34,093 | ​ |  | 34,613
Due after five years through ten years | ​ |  | 103,411 | ​ |  | 100,798 | ​ |  | 45,919 | ​ |  | 45,263
Due after ten years | ​ |  | 686,474 | ​ |  | 658,478 | ​ |  | 754,301 | ​ |  | 725,140
Total HTM securities | ​ | $ | 807,080 | ​ | $ | 776,827 | ​ | $ | 837,378 | ​ | $ | 808,074
Schedule of Carrying Values, Gross Unrealized Gains and Losses and Estimated Fair Value of Securities | ​ The Company reports HTM securities on the Company’s Consolidated Balance Sheets at carrying value. Carrying value is amortized cost, which includes any unamortized unrealized gains and losses recognized in AOCI prior to reclassifying the securities from AFS securities to HTM securities. The carrying value, gross unrealized gains and losses, and estimated fair values of HTM securities as of September 30, 2024 are as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Carrying | ​ | Gross Unrealized | ​ | Estimated
​ |  | Value |  | Gains |  | (Losses) | ​ | Fair Value
September 30, 2024 | ​ | ​ |  |  | ​ |  |  | ​ |  | ​ | ​ |
Obligations of states and political subdivisions | ​ | $ | 695,460 | ​ | $ | 3,775 | ​ | $ | (23,241) | ​ | $ | 675,994
Corporate and other bonds(1) | ​ | ​ | 3,484 | ​ | ​ | — | ​ | ​ | (64) | ​ | ​ | 3,420
Commercial MBS | ​ |  | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 27,164 | ​ | ​ | — | ​ | ​ | (5,308) | ​ | ​ | 21,856
Non-agency | ​ | ​ | 21,218 | ​ | ​ | 156 | ​ | ​ | (533) | ​ | ​ | 20,841
Total commercial MBS | ​ | ​ | 48,382 | ​ | ​ | 156 | ​ | ​ | (5,841) | ​ | ​ | 42,697
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 38,339 | ​ | ​ | — | ​ | ​ | (4,872) | ​ | ​ | 33,467
Non-agency | ​ | ​ | 21,415 | ​ | ​ | 15 | ​ | ​ | (181) | ​ | ​ | 21,249
Total residential MBS | ​ | ​ | 59,754 | ​ | ​ | 15 | ​ | ​ | (5,053) | ​ | ​ | 54,716
Total HTM securities | ​ | $ | 807,080 | ​ | $ | 3,946 | ​ | $ | (34,199) | ​ | $ | 776,827
(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, 2023 are as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Carrying | ​ | Gross Unrealized | ​ | Estimated
​ |  | Value |  | Gains |  | (Losses) |  | Fair Value
December 31, 2023 | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |
Obligations of states and political subdivisions | ​ | $ | 699,189 | ​ | $ | 6,175 | ​ | $ | (23,464) | ​ | $ | 681,900
Corporate and other bonds(1) | ​ | ​ | 4,349 | ​ | ​ | — | ​ | ​ | (100) | ​ | ​ | 4,249
Commercial MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 27,477 | ​ | ​ | — | ​ | ​ | (5,570) | ​ | ​ | 21,907
Non-agency | ​ | ​ | 24,503 | ​ | ​ | 37 | ​ | ​ | (449) | ​ | ​ | 24,091
Total commercial MBS | ​ | ​ | 51,980 | ​ | ​ | 37 | ​ | ​ | (6,019) | ​ | ​ | 45,998
Residential MBS | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Agency | ​ | ​ | 40,562 | ​ | ​ | — | ​ | ​ | (5,713) | ​ | ​ | 34,849
Non-agency | ​ | ​ | 41,298 | ​ | ​ | 122 | ​ | ​ | (342) | ​ | ​ | 41,078
Total residential MBS | ​ | ​ | 81,860 | ​ | ​ | 122 | ​ | ​ | (6,055) | ​ | ​ | 75,927
Total HTM securities | ​ | $ | 837,378 | ​ | $ | 6,334 | ​ | $ | (35,638) | ​ | $ | 808,074
(1) Other bonds include asset-backed securities.

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