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Investments (Summary Of Net Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Gain (Loss) on Securities [Line Items]
Net realized investment gains (losses)	$ (36,093)	$ 2,032	$ (38,159)	$ 6,001
Equity securities, Change in fair value of securities sold during the period	2,683	2,553	16,706	(29,015)
Equity securities, Change in fair value of securities held at the end of the period	(232,507)	(286,068)	612,626	(2,171,511)
Total change in fair value of equity securities	(229,824)	(283,515)	629,332	(2,200,526)
Net investment gains (losses)	(265,917)	(281,483)	591,173	(2,194,525)
Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive loss:	(208,405)	(538,347)	(170,606)	(1,656,623)
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive loss:	(208,598)	(530,161)	(167,411)	(1,645,060)
Short-term investments [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains (losses) on available-for-sale investments included in other comprehensive loss:	$ 193	$ (8,186)	$ (3,195)	$ (11,563)

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The net gains or losses on investments during the period, also including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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