Investments (Summary Of Net Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Gain (Loss) on Securities [Line Items]
Cost method investments, realized gains	$ 0	$ 0	$ 11,167	$ 0
Net realized investment gains (losses)	(2,812)	(67)	6,926	614
Change in fair value of equity securities sold during the period	82,523	202	43,458	26,616
Change in fair value of equity securities held at the end of the period	831,532	425,518	(820,582)	1,010,614
Total change in fair value of equity securities	914,055	425,720	(777,124)	1,037,230
Net investment gains (losses)	911,243	425,653	(770,198)	1,037,844
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	216,909	163,816	295,898	356,652
Reserve deficiency adjustment for life and annuity benefit reserves	(22,740)	(35,938)	(35,612)	(61,751)
Sales of fixed maturities [Member]
Gain (Loss) on Securities [Line Items]
Fixed maturity securities, realized gains	5,348	1,661	6,733	1,804
Fixed maturity securities, realized losses	(5,126)	(630)	(6,271)	(911)
Change in allowance for expected credit losses	1,537	0	(202)	0
Sales of short-term investments [Member]
Gain (Loss) on Securities [Line Items]
Short-term investments, available-for-sale, realized gain	1,002	499	1,100	1,334
Short-term investments, available-for-sale, realized loss	(184)	(2,049)	(356)	(2,073)
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	236,521	197,248	335,088	414,542
Short-term investments [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	3,128	2,506	(3,578)	3,861
Sales of Other Investments
Gain (Loss) on Securities [Line Items]
Other investment gains (losses)	$ (5,389)	$ 452	$ (5,245)	$ 460

Change in the fair value of equity securities held at the end of the period.

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Amount of realized gain on cost method investments recognized in other comprehensive income.

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Change in net unrealized holding gains included in other comprehensive income for the adjustment for life and annuity benefits reserves, before tax

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Amount of expense for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), for which no credit loss was previously recorded.

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount before tax, after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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