Investments (Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	$ 2,030,690	$ 697,102
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(76,054)	(13,139)
Available-for-sale securities, estimated fair value, 12 months or longer	813,147	1,333,930
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(19,842)	(22,079)
Available-for-sale securities, estimated fair value	2,843,837	2,031,032
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(95,896)	(35,218)
U.S. Treasury Securities And Obligations Of U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	427,003	108,250
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(3,648)	(62)
Available-for-sale securities, estimated fair value, 12 months or longer	92,552	163,359
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(1,133)	(2,101)
Available-for-sale securities, estimated fair value	519,555	271,609
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(4,781)	(2,163)
Obligations Of States, Municipalities And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	169,362	58,583
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(4,864)	(542)
Available-for-sale securities, estimated fair value, 12 months or longer	70,101	92,441
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(3,361)	(2,817)
Available-for-sale securities, estimated fair value	239,463	151,024
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(8,225)	(3,359)
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	51,328	18,856
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(249)	(386)
Available-for-sale securities, estimated fair value, 12 months or longer	40,345	56,217
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(1,432)	(655)
Available-for-sale securities, estimated fair value	91,673	75,073
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(1,681)	(1,041)
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	289,058	45,931
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(3,600)	(210)
Available-for-sale securities, estimated fair value, 12 months or longer	95,843	147,558
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(1,399)	(2,392)
Available-for-sale securities, estimated fair value	384,901	193,489
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(4,999)	(2,602)
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	78,814	9,613
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(2,858)	(2,285)
Available-for-sale securities, estimated fair value, 12 months or longer	137,100	207,374
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(3,422)	(3,455)
Available-for-sale securities, estimated fair value	215,914	216,987
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(6,280)	(5,740)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	6,228	30,448
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(54)	(20)
Available-for-sale securities, estimated fair value, 12 months or longer	24,315	45,160
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(352)	(662)
Available-for-sale securities, estimated fair value	30,543	75,608
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(406)	(682)
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	470,694	141,176
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(9,509)	(2,263)
Available-for-sale securities, estimated fair value, 12 months or longer	343,737	621,821
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(8,324)	(9,997)
Available-for-sale securities, estimated fair value	814,431	762,997
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(17,833)	(12,260)
Total Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	1,492,487	412,857
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(24,782)	(5,768)
Available-for-sale securities, estimated fair value, 12 months or longer	803,993	1,333,930
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(19,423)	(22,079)
Available-for-sale securities, estimated fair value	2,296,480	1,746,787
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(44,205)	(27,847)
Insurance, Banks And Other Financial Institutions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	63,873	16,219
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(6,384)	(1,531)
Available-for-sale securities, estimated fair value, 12 months or longer	6,247	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(167)	0
Available-for-sale securities, estimated fair value	70,120	16,219
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(6,551)	(1,531)
Industrial, Consumer And All Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	344,857	86,062
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(44,879)	(5,834)
Available-for-sale securities, estimated fair value, 12 months or longer	2,907	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(252)	0
Available-for-sale securities, estimated fair value	347,764	86,062
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(45,131)	(5,834)
Total Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	408,730	102,281
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(51,263)	(7,365)
Available-for-sale securities, estimated fair value, 12 months or longer	9,154	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(419)	0
Available-for-sale securities, estimated fair value	417,884	102,281
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	(51,682)	(7,365)
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	129,473	181,964
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, less than 12 months	(9)	(6)
Available-for-sale securities, estimated fair value, 12 months or longer	0	0
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	0	0
Available-for-sale securities, estimated fair value	129,473	181,964
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (9)	$ (6)