Investments (Summary Of Net Realized Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Gain (Loss) on Investments [Line Items]
Realized gains	$ 13,831	$ 22,539	$ 35,974	$ 69,706
Realized losses	(5,461)	(4,302)	(11,409)	(22,332)
Gains (losses) on securities measured at fair value through net income (loss)	(48,377)	9,179	(26,080)	18,462
Other-than-temporary impairment losses recognized in net income	(3,444)	0	(7,261)	(12,080)
Net realized investment gains (losses)	(40,007)	27,416	(1,515)	65,836
Change in net unrealized gains on investments included in other comprehensive income	328,768	26,381	836,258	619,072
Sales Of Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	3,426	3,698	4,189	4,658
Realized losses	(663)	(60)	(1,271)	(608)
Sales Of Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	9,276	18,418	25,806	63,931
Realized losses	(578)	(4,187)	(1,791)	(6,672)
Other [Member]
Gain (Loss) on Investments [Line Items]
Realized gains	1,129	423	5,979	1,117
Realized losses	(776)	(55)	(1,086)	(2,972)
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments included in other comprehensive income	20,428	(53,962)	104,488	399,020
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments included in other comprehensive income	308,324	80,285	731,748	220,029
Short-Term Investments [Member]
Gain (Loss) on Investments [Line Items]
Change in net unrealized gains on investments included in other comprehensive income	$ 16	$ 58	$ 22	$ 23