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Investments (Tables)

12 Months Ended

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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