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Investments (Tables)

12 Months Ended

Dec. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Available-For-Sale Investments

a) The following tables summarize the Company's available-for-sale investments. Agency 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, 2024
(dollars in thousands)			Amortized Cost						Gross Unrealized Holding Gains						Gross Unrealized Holding Losses						Estimated Fair Value
Fixed maturity securities:
U.S. Treasury securities			$	5,147,365					$	8,962					$	(68,469)					$	5,087,858
U.S. government-sponsored enterprises			1,445,171						2,976						(101,911)						1,346,236
Obligations of states, municipalities and political subdivisions			3,813,146						5,866						(199,520)						3,619,492
Foreign governments, agencies and supranationals			2,909,561						4,264						(207,302)						2,706,523
Agency mortgage-backed securities			2,771,589						2,096						(123,872)						2,649,813
Non-agency mortgage-backed securities			122,373						—						(4,343)						118,030
Corporate and university bonds			248,518						76						(31,007)						217,587
Total fixed maturity securities			16,457,723						24,240						(736,424)						15,745,539
Short-term investments			2,530,941						548						(6,579)						2,524,910
Investments, available-for-sale			$	18,988,664					$	24,788					$	(743,003)					$	18,270,449

			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, agencies and supranationals			2,554,874						34,352						(142,008)						2,447,218
Agency mortgage-backed securities			2,507,682						8,939						(135,611)						2,381,010
Non-agency mortgage-backed securities			355,673						—						(22,603)						333,070
Corporate and university bonds			281,242						141						(26,781)						254,602
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

Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position

b) 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, 2024
			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			$	1,593,711					$	(27,213)					$	1,444,869					$	(41,256)					$	3,038,580					$	(68,469)
U.S. government-sponsored enterprises			415,333						(10,938)						691,781						(90,973)						1,107,114						(101,911)
Obligations of states, municipalities and political subdivisions			1,133,275						(21,242)						2,024,298						(178,278)						3,157,573						(199,520)
Foreign governments, agencies and supranationals			1,056,877						(29,890)						1,246,215						(177,412)						2,303,092						(207,302)
Agency mortgage-backed securities			757,562						(13,880)						1,710,436						(109,992)						2,467,998						(123,872)
Non-agency mortgage-backed securities			—						—						118,030						(4,343)						118,030						(4,343)
Corporate and university bonds			2,107						(137)						212,404						(30,870)						214,511						(31,007)
Total fixed maturity securities			4,958,865						(103,300)						7,448,033						(633,124)						12,406,898						(736,424)
Short-term investments			163,503						(6,579)						—						—						163,503						(6,579)
Total			$	5,122,368					$	(109,879)					$	7,448,033					$	(633,124)					$	12,570,401					$	(743,003)

			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, agencies and supranationals			83,396						(394)						1,492,912						(141,614)						1,576,308						(142,008)
Agency mortgage-backed securities			189,977						(1,872)						1,889,272						(133,739)						2,079,249						(135,611)
Non-agency mortgage-backed securities			—						—						333,070						(22,603)						333,070						(22,603)
Corporate and university bonds			—						—						236,205						(26,781)						236,205						(26,781)
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)

Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity

c) The amortized cost and estimated fair value of fixed maturity securities at December 31, 2024 are shown below by contractual maturity.

(dollars in thousands)			Amortized Cost						Estimated Fair Value
Due in one year or less			$	1,593,149					$	1,571,022
Due after one year through five years			6,071,013						5,901,682
Due after five years through ten years			4,647,538						4,406,225
Due after ten years			1,252,061						1,098,767
			13,563,761						12,977,696
Mortgage-backed securities			2,893,962						2,767,843
Total fixed maturity securities			$	16,457,723					$	15,745,539

Components Of Net Investment Income

d) The following table presents the components of net investment income.

			Years Ended December 31,
(dollars in thousands)			2024						2023						2022
Interest:
Fixed maturity securities			$	510,044					$	383,022					$	294,417
Short-term investments			124,575						106,747						33,493
Cash and cash equivalents and restricted cash and cash equivalents			161,488						145,074						28,890
Dividends on equity securities			142,367						116,911						107,213
			938,474						751,754						464,013
Investment expenses			(17,978)						(17,222)						(17,258)
Net investment income			$	920,496					$	734,532					$	446,755

Summary Of Net Realized Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments

e) The following table presents the components of net investment gains (losses) included in net income (loss) and the pre-tax change in net unrealized 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)			2024						2023						2022
Fixed maturity securities, short-term investments and other investments:
Net realized investment gains (losses)			$	4,423					$	(42,177)					$	(40,983)
Equity securities:
Change in fair value of securities sold during the period			(14,966)						34,684						(14,884)
Change in fair value of securities held at the end of the period			1,817,762						1,531,547						(1,539,866)
Total change in fair value			1,802,796						1,566,231						(1,554,750)
Net investment gains (losses)			$	1,807,219					$	1,524,054					$	(1,595,733)
Change in net unrealized losses on available-for-sale investments included in other comprehensive income (loss):
Fixed maturity securities			$	(152,630)					$	389,498					$	(1,474,890)
Short-term investments			(12,793)						1,060						11,014
Net increase (decrease)			$	(165,423)					$	390,558					$	(1,463,876)

Schedule of Restricted Assets

f) Total restricted assets are included on the Company's consolidated balance sheets as follows.

			December 31,
(dollars in thousands)			2024						2023
Fixed maturity securities			$	3,027,863					$	3,102,899
Equity securities			915,242						1,004,347
Short-term investments			704,201						807,138
Restricted cash and cash equivalents			499,581						584,974
Total			$	5,146,887					$	5,499,358

Components Of Restricted Assets

The following table presents the components of restricted assets.

			December 31,
(dollars in thousands)			2024						2023
Assets held in trust or on deposit to support underwriting activities			$	4,727,799					$	5,048,857
Assets pledged as security for letters of credit			419,088						450,501
Total			$	5,146,887					$	5,499,358

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