Investments (Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	$ 5,763,958	$ 1,467,268
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(33,219)	(10,821)
Available-for-sale securities, estimated fair value, 12 months or longer	8,290,674	8,515,061
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(717,115)	(650,461)
Available-for-sale securities, estimated fair value	14,054,632	9,982,329
Available-for-sale securities, gross unrealized holding losses	(750,334)	(661,282)
Short-term investments, estimated fair value, less than 12 months	2,272,608	52,601
Short-term investments, gross unrealized holding losses, less than 12 months	(1,117)	(393)
Short-term investments, estimated fair value, 12 months or longer	0	0
Short-term investments, gross unrealized holding losses, 12 months or longer	0	0
Short-term investments, estimated fair value	2,272,608	52,601
Short-term investments, gross unrealized holding losses	(1,117)	(393)
Fixed maturities, available-for-sale, amortized cost	15,227,752	14,932,286
Available-for-sale fixed maturity investments, gross unrealized holding gains	40,835	101,335
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(749,217)	(660,889)
Available-for-sale fixed maturity investments, estimated fair value	14,519,370	14,372,732
U.S. Treasury securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	1,553,613	317,027
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(10,383)	(2,147)
Available-for-sale securities, estimated fair value, 12 months or longer	1,388,322	1,507,784
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(69,025)	(60,257)
Available-for-sale securities, estimated fair value	2,941,935	1,824,811
Available-for-sale securities, gross unrealized holding losses	(79,408)	(62,404)
Fixed maturities, available-for-sale, amortized cost	4,113,319	3,811,293
Available-for-sale fixed maturity investments, gross unrealized holding gains	12,079	35,824
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(79,408)	(62,404)
Available-for-sale fixed maturity investments, estimated fair value	4,045,990	3,784,713
U.S. government-sponsored enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	244,720	145,143
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(3,629)	(2,134)
Available-for-sale securities, estimated fair value, 12 months or longer	746,832	723,537
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(95,801)	(87,770)
Available-for-sale securities, estimated fair value	991,552	868,680
Available-for-sale securities, gross unrealized holding losses	(99,430)	(89,904)
Fixed maturities, available-for-sale, amortized cost	1,289,119	1,225,426
Available-for-sale fixed maturity investments, gross unrealized holding gains	4,206	7,292
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(99,430)	(89,904)
Available-for-sale fixed maturity investments, estimated fair value	1,193,895	1,142,814
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	920,869	679,124
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(8,138)	(3,881)
Available-for-sale securities, estimated fair value, 12 months or longer	2,376,770	2,332,281
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(197,178)	(177,697)
Available-for-sale securities, estimated fair value	3,297,639	3,011,405
Available-for-sale securities, gross unrealized holding losses	(205,316)	(181,578)
Fixed maturities, available-for-sale, amortized cost	4,041,845	4,196,096
Available-for-sale fixed maturity investments, gross unrealized holding gains	10,059	14,787
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(205,316)	(181,578)
Available-for-sale fixed maturity investments, estimated fair value	3,846,588	4,029,305
Foreign governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	322,098	49,056
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(3,059)	(128)
Available-for-sale securities, estimated fair value, 12 months or longer	1,079,889	1,113,616
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(123,871)	(96,746)
Available-for-sale securities, estimated fair value	1,401,987	1,162,672
Available-for-sale securities, gross unrealized holding losses	(126,930)	(96,874)
Fixed maturities, available-for-sale, amortized cost	1,950,839	1,858,845
Available-for-sale fixed maturity investments, gross unrealized holding gains	4,132	21,450
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(126,930)	(96,874)
Available-for-sale fixed maturity investments, estimated fair value	1,828,041	1,783,421
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	275,805	169,557
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(4,101)	(1,792)
Available-for-sale securities, estimated fair value, 12 months or longer	1,722,270	1,790,637
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(133,371)	(134,561)
Available-for-sale securities, estimated fair value	1,998,075	1,960,194
Available-for-sale securities, gross unrealized holding losses	(137,472)	(136,353)
Fixed maturities, available-for-sale, amortized cost	2,400,848	2,371,406
Available-for-sale fixed maturity investments, gross unrealized holding gains	4,780	8,605
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(137,472)	(136,353)
Available-for-sale fixed maturity investments, estimated fair value	2,268,156	2,243,658
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	25,905	20,420
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(456)	(80)
Available-for-sale securities, estimated fair value, 12 months or longer	401,845	431,705
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(21,731)	(21,781)
Available-for-sale securities, estimated fair value	427,750	452,125
Available-for-sale securities, gross unrealized holding losses	(22,187)	(21,861)
Fixed maturities, available-for-sale, amortized cost	463,710	491,949
Available-for-sale fixed maturity investments, gross unrealized holding gains	155	334
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(22,187)	(21,861)
Available-for-sale fixed maturity investments, estimated fair value	441,678	470,422
Corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	148,340	34,340
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(2,336)	(266)
Available-for-sale securities, estimated fair value, 12 months or longer	574,746	615,501
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(76,138)	(71,649)
Available-for-sale securities, estimated fair value	723,086	649,841
Available-for-sale securities, gross unrealized holding losses	(78,474)	(71,915)
Fixed maturities, available-for-sale, amortized cost	968,072	977,271
Available-for-sale fixed maturity investments, gross unrealized holding gains	5,424	13,043
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(78,474)	(71,915)
Available-for-sale fixed maturity investments, estimated fair value	895,022	918,399
Total fixed maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	3,491,350	1,414,667
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(32,102)	(10,428)
Available-for-sale securities, estimated fair value, 12 months or longer	8,290,674	8,515,061
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(717,115)	(650,461)
Available-for-sale securities, estimated fair value	11,782,024	9,929,728
Available-for-sale securities, gross unrealized holding losses	$ (749,217)	$ (660,889)

Amount of short-term investment measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

No definition available.