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, 2019	Mar. 31, 2018
Gain (Loss) on Securities [Line Items]
Realized Gains	$ 1,743	$ 3,895
Realized Losses	1,062	4,841
Net realized investment gains (losses)	681	(946)
Change in fair value of equity securities sold during the period	10,558	5,130
Change in fair value of equity securities held at the end of the period	600,952	(127,182)
Change in fair value of equity securities	611,510	(122,052)
Net investment gains (losses)	612,191	(122,998)
Change in net unrealized gains on available-for-sale investments included in other comprehensive income (loss)	218,649	(144,121)
Sales Of Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Realized Gains	144	141
Realized Losses	280	952
Sales Of Short-Term Investments [Member]
Gain (Loss) on Securities [Line Items]
Realized Gains	1,591	2,865
Realized Losses	(782)	(1,158)
Other [Member]
Gain (Loss) on Securities [Line Items]
Realized Gains	8	889
Realized Losses	0	2,731
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)	217,294	(144,168)
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)	$ 1,355	$ 47