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Investments (Tables) | 12 Months Ended
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Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract] |
Available-For-Sale Investments | The following tables summarize the Company's available-for-sale investments. Commercial and residential mortgage-backed securities include securities issued by U.S. government-sponsored enterprises and U.S. government agencies. The net unrealized holding gains (losses) in the tables below are presented before taxes.
| December 31, 2023
(dollars in thousands) | Amortized Cost |  | Gross Unrealized Holding Gains |  | Gross Unrealized Holding Losses |  |  |  | Estimated Fair Value
Fixed maturity securities: |  |  |  |  |  |  |  |  |
U.S. Treasury securities | $ | 3,811,293 |  |  | $ | 35,824 |  |  | $ | (62,404) |  |  |  |  | $ | 3,784,713 |
U.S. government-sponsored enterprises | 1,225,426 |  |  | 7,292 |  |  | (89,904) |  |  |  |  | 1,142,814 |
Obligations of states, municipalities and political subdivisions | 4,196,096 |  |  | 14,787 |  |  | (181,578) |  |  |  |  | 4,029,305 |
Foreign governments | 1,858,845 |  |  | 21,450 |  |  | (96,874) |  |  |  |  | 1,783,421 |
Commercial mortgage-backed securities | 2,371,406 |  |  | 8,605 |  |  | (136,353) |  |  |  |  | 2,243,658 |
Residential mortgage-backed securities | 491,949 |  |  | 334 |  |  | (21,861) |  |  |  |  | 470,422 |
Corporate bonds | 977,271 |  |  | 13,043 |  |  | (71,915) |  |  |  |  | 918,399 |
Total fixed maturity securities | 14,932,286 |  |  | 101,335 |  |  | (660,889) |  |  |  |  | 14,372,732 |
Short-term investments | 2,564,620 |  |  | 7,155 |  |  | (393) |  |  |  |  | 2,571,382 |
Investments, available-for-sale | $ | 17,496,906 |  |  | $ | 108,490 |  |  | $ | (661,282) |  |  |  |  | $ | 16,944,114 |
| December 31, 2022
(dollars in thousands) | Amortized Cost |  | Gross Unrealized Holding Gains |  | Gross Unrealized Holding Losses |  | Estimated Fair Value
Fixed maturity securities: |  |  |  |  |  |  |
U.S. Treasury securities | $ | 3,050,089 |  |  | $ | 2,363 |  |  | $ | (138,493) |  |  | $ | 2,913,959 |
U.S. government-sponsored enterprises | 871,463 |  |  | 154 |  |  | (106,079) |  |  | 765,538 |
Obligations of states, municipalities and political subdivisions | 3,973,911 |  |  | 6,503 |  |  | (247,231) |  |  | 3,733,183 |
Foreign governments | 1,473,658 |  |  | 2,843 |  |  | (169,723) |  |  | 1,306,778 |
Commercial mortgage-backed securities | 2,109,721 |  |  | 395 |  |  | (169,668) |  |  | 1,940,448 |
Residential mortgage-backed securities | 553,591 |  |  | 6 |  |  | (26,804) |  |  | 526,793 |
Corporate bonds | 773,454 |  |  | 836 |  |  | (104,154) |  |  | 670,136 |
Total fixed maturity securities | 12,805,887 |  |  | 13,100 |  |  | (962,152) |  |  | 11,856,835 |
Short-term investments | 2,663,560 |  |  | 5,760 |  |  | (58) |  |  | 2,669,262 |
Investments, available-for-sale | $ | 15,469,447 |  |  | $ | 18,860 |  |  | $ | (962,210) |  |  | $ | 14,526,097 |
Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position | The following tables summarize gross unrealized investment losses on available-for-sale investments by the length of time that securities have continuously been in an unrealized loss position.
| December 31, 2023
| Less than 12 months |  | 12 months or longer |  | Total
(dollars in thousands) | Estimated Fair Value |  | Gross Unrealized Holding Losses |  | Estimated Fair Value |  | Gross Unrealized Holding Losses |  | Estimated Fair Value |  | Gross Unrealized Holding Losses
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury securities | $ | 317,027 |  |  | $ | (2,147) |  |  | $ | 1,507,784 |  |  | $ | (60,257) |  |  | $ | 1,824,811 |  |  | $ | (62,404) |
U.S. government-sponsored enterprises | 145,143 |  |  | (2,134) |  |  | 723,537 |  |  | (87,770) |  |  | 868,680 |  |  | (89,904) |
Obligations of states, municipalities and political subdivisions | 679,124 |  |  | (3,881) |  |  | 2,332,281 |  |  | (177,697) |  |  | 3,011,405 |  |  | (181,578) |
Foreign governments | 49,056 |  |  | (128) |  |  | 1,113,616 |  |  | (96,746) |  |  | 1,162,672 |  |  | (96,874) |
Commercial mortgage-backed securities | 169,557 |  |  | (1,792) |  |  | 1,790,637 |  |  | (134,561) |  |  | 1,960,194 |  |  | (136,353) |
Residential mortgage-backed securities | 20,420 |  |  | (80) |  |  | 431,705 |  |  | (21,781) |  |  | 452,125 |  |  | (21,861) |
Corporate bonds | 34,340 |  |  | (266) |  |  | 615,501 |  |  | (71,649) |  |  | 649,841 |  |  | (71,915) |
Total fixed maturity securities | 1,414,667 |  |  | (10,428) |  |  | 8,515,061 |  |  | (650,461) |  |  | 9,929,728 |  |  | (660,889) |
Short-term investments | 52,601 |  |  | (393) |  |  | — |  |  | — |  |  | 52,601 |  |  | (393) |
Total | $ | 1,467,268 |  |  | $ | (10,821) |  |  | $ | 8,515,061 |  |  | $ | (650,461) |  |  | $ | 9,982,329 |  |  | $ | (661,282) |
| December 31, 2022
| Less than 12 months |  | 12 months or longer |  | Total
(dollars in thousands) | Estimated Fair Value |  | Gross Unrealized Holding Losses |  | Estimated Fair Value |  | Gross Unrealized Holding Losses |  | Estimated Fair Value |  | Gross Unrealized Holding Losses
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury securities | $ | 735,605 |  |  | $ | (30,583) |  |  | $ | 1,907,922 |  |  | $ | (107,910) |  |  | $ | 2,643,527 |  |  | $ | (138,493) |
U.S. government-sponsored enterprises | 413,495 |  |  | (40,488) |  |  | 331,391 |  |  | (65,591) |  |  | 744,886 |  |  | (106,079) |
Obligations of states, municipalities and political subdivisions | 2,474,289 |  |  | (164,537) |  |  | 348,943 |  |  | (82,694) |  |  | 2,823,232 |  |  | (247,231) |
Foreign governments | 900,322 |  |  | (115,324) |  |  | 300,423 |  |  | (54,399) |  |  | 1,200,745 |  |  | (169,723) |
Commercial mortgage-backed securities | 1,611,603 |  |  | (117,482) |  |  | 305,217 |  |  | (52,186) |  |  | 1,916,820 |  |  | (169,668) |
Residential mortgage-backed securities | 516,423 |  |  | (25,232) |  |  | 9,342 |  |  | (1,572) |  |  | 525,765 |  |  | (26,804) |
Corporate bonds | 498,406 |  |  | (74,595) |  |  | 153,035 |  |  | (29,559) |  |  | 651,441 |  |  | (104,154) |
Total fixed maturity securities | 7,150,143 |  |  | (568,241) |  |  | 3,356,273 |  |  | (393,911) |  |  | 10,506,416 |  |  | (962,152) |
Short-term investments | 774,480 |  |  | (58) |  |  | — |  |  | — |  |  | 774,480 |  |  | (58) |
Total | $ | 7,924,623 |  |  | $ | (568,299) |  |  | $ | 3,356,273 |  |  | $ | (393,911) |  |  | $ | 11,280,896 |  |  | $ | (962,210) |
Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity | The amortized cost and estimated fair value of fixed maturity securities at December 31, 2023 are shown below by contractual maturity.
(dollars in thousands) | Amortized Cost |  | Estimated Fair Value
Due in one year or less | $ | 1,192,021 |  |  | $ | 1,179,344 |
Due after one year through five years | 5,033,324 |  |  | 4,917,770 |
Due after five years through ten years | 4,320,467 |  |  | 4,159,846 |
Due after ten years | 1,523,119 |  |  | 1,401,692 |
| 12,068,931 |  |  | 11,658,652 |
Commercial mortgage-backed securities | 2,371,406 |  |  | 2,243,658 |
Residential mortgage-backed securities | 491,949 |  |  | 470,422 |
Total fixed maturity securities | $ | 14,932,286 |  |  | $ | 14,372,732 |
Components Of Net Investment Income | The following table presents the components of net investment income.
| Years Ended December 31,
(dollars in thousands) | 2023 |  | 2022 |  | 2021
Interest: |  |  |  |  |
Fixed maturity securities | $ | 383,022 |  |  | $ | 294,417 |  |  | $ | 283,366 |
Short-term investments | 106,747 |  |  | 33,493 |  |  | 2,475 |
Cash and cash equivalents | 145,074 |  |  | 28,890 |  |  | 479 |
Dividends on equity securities | 116,911 |  |  | 107,213 |  |  | 98,099 |
| 751,754 |  |  | 464,013 |  |  | 384,419 |
Investment expenses | (17,222) |  |  | (17,258) |  |  | (17,002) |
Net investment income | $ | 734,532 |  |  | $ | 446,755 |  |  | $ | 367,417 |
Summary Of Net Realized Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments | The following table presents the components of net investment gains (losses) included in net income (loss) and the pre-tax change in net unrealized gains (losses) included in other comprehensive income (loss). Gross realized investment gains and losses on fixed maturity securities, short-term investments and other investments were not material to the consolidated financial statements and are presented on a net basis in the following table.
| Years Ended December 31,
(dollars in thousands) | 2023 |  | 2022 |  | 2021
Fixed maturity securities, short-term investments and other investments: |  |  |  |  |
Net realized investment gains (losses) | $ | (42,177) |  |  | $ | (40,983) |  |  | $ | 37,908 |
Equity securities: |  |  |  |  |
Change in fair value of securities sold during the period | 34,684 |  |  | (14,884) |  |  | 25,902 |
Change in fair value of securities held at the end of the period | 1,531,547 |  |  | (1,539,866) |  |  | 1,914,724 |
Total change in fair value | 1,566,231 |  |  | (1,554,750) |  |  | 1,940,626 |
Net investment gains (losses) | $ | 1,524,054 |  |  | $ | (1,595,733) |  |  | $ | 1,978,534 |
Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive income (loss): |  |  |  |  |
Fixed maturity securities | $ | 389,498 |  |  | $ | (1,474,890) |  |  | $ | (504,133) |
Short-term investments | 1,060 |  |  | 11,014 |  |  | (8,951) |
Net increase (decrease) | $ | 390,558 |  |  | $ | (1,463,876) |  |  | $ | (513,084) |
Schedule of Restricted Assets | Total restricted assets are included on the Company's consolidated balance sheets as follows.
| December 31,
(dollars in thousands) | 2023 |  | 2022
Fixed maturity securities | $ | 3,102,899 |  |  | $ | 2,773,386 |
Equity securities | 1,004,347 |  |  | 843,719 |
Short-term investments | 807,138 |  |  | 543,737 |
Restricted cash and cash equivalents | 584,974 |  |  | 1,084,081 |
Total | $ | 5,499,358 |  |  | $ | 5,244,923 |
Components Of Restricted Assets | The following table presents the components of restricted assets.
| December 31,
(dollars in thousands) | 2023 |  | 2022
Assets held in trust or on deposit to support underwriting activities | $ | 5,048,857 |  |  | $ | 4,807,135 |
Assets pledged as security for letters of credit | 450,501 |  |  | 437,788 |
Total | $ | 5,499,358 |  |  | $ | 5,244,923 |

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