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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Gain (Loss) on Securities [Line Items]
Document Period End Date			Sep. 30, 2019
Realized gains	$ 2,520	$ 4,534	$ 4,532	$ 6,380
Realized losses	(2,370)	(5,030)	(3,768)	(15,464)
Net realized investment gains (losses)	150	(496)	764	(9,084)
Change in fair value of equity securities sold during the period	(345)	151	35,786	10,230
Change in fair value of equity securities held at the end of the period	32,339	426,420	1,033,438	407,180
Change in fair value of equity securities	31,994	426,571	1,069,224	417,410
Net investment gains	32,144	426,075	1,069,988	408,326
Change in net unrealized gains on available-for-sale investments included in other comprehensive income (loss)	92,904	(101,666)	511,307	(383,937)
Sales of fixed maturities [Member]
Gain (Loss) on Securities [Line Items]
Realized gains	856	2,916	2,660	3,748
Realized losses	(198)	(1,003)	(1,109)	(2,652)
Sales of short-term investments [Member]
Gain (Loss) on Securities [Line Items]
Short-term investments, available-for-sale, realized gain	1,540	1,447	1,288	1,624
Short-term investments, available-for-sale, realized loss	(2,172)	(3,997)	(2,659)	(10,044)
Other [Member]
Gain (Loss) on Securities [Line Items]
Realized gains	124	171	584	1,008
Realized losses	0	(30)	0	(2,768)
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)	95,170	(103,083)	509,712	(384,176)
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)	$ (2,266)	$ 1,417	$ 1,595	$ 239