Investments (Summary Of Net Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Gain (Loss) on Securities [Line Items]
Realized gains	$ 14,399	$ 1,743
Cost method investments, realized gain	11,167	0
Realized losses	(4,661)	(1,062)
Net realized investment gains	9,738	681
Change in fair value of equity securities sold during the period	(39,065)	10,558
Change in fair value of equity securities held at the end of the period	(1,652,114)	600,952
Change in fair value of equity securities	(1,691,179)	611,510
Net investment gains (losses)	(1,681,441)	612,191
Change in net unrealized gains on available-for-sale investments included in other comprehensive income (loss)	78,989	192,836
Reserve deficiency adjustment for life and annuity benefit reserves	(12,872)	(25,813)
Sales of fixed maturities [Member]
Gain (Loss) on Securities [Line Items]
Realized gains	1,385	144
Realized losses	(2,884)	(280)
Sales of short-term investments [Member]
Gain (Loss) on Securities [Line Items]
Short-term investments, available-for-sale, realized gain	98	1,591
Short-term investments, available-for-sale, realized loss	(172)	(782)
Other [Member]
Gain (Loss) on Securities [Line Items]
Realized gains	1,749	8
Realized losses	(1,605)	0
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income (loss)	98,567	217,294
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 (loss)	$ (6,706)	$ 1,355