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, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		$ 2,610,752
Available-for-sale securities, estimated fair value, less than 12 months			$ 1,286,311
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(56,485)
Available-for-sale securities, gross unrealized holding losses, less than 12 months			(23,000)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		1,983,912
Available-for-sale securities, estimated fair value, 12 months or longer			1,481,341
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(77,504)
Available-for-sale securities, gross unrealized holding losses, 12 months or longer			(34,348)
Available-for-sale fixed maturity securities, estimated fair value		4,594,664
Available-for-sale securities, estimated fair value			2,767,652
Available-for-sale fixed maturity securities, gross unrealized holding losses		(133,989)
Available-for-sale securities, gross unrealized holding losses			(57,348)
U.S. Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		2,922	78,756
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(83)	(659)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		156,352	78,298
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(1,869)	(1,160)
Available-for-sale fixed maturity securities, estimated fair value		159,274	157,054
Available-for-sale fixed maturity securities, gross unrealized holding losses		(1,952)	(1,819)
U.S. Government-Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		88,854	11,593
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(1,923)	(79)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		96,337	89,194
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(2,191)	(739)
Available-for-sale fixed maturity securities, estimated fair value		185,191	100,787
Available-for-sale fixed maturity securities, gross unrealized holding losses		(4,114)	(818)
Obligations Of States, Municipalities And Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		656,573	80,654
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(12,455)	(789)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		453,736	404,814
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(16,413)	(7,127)
Available-for-sale fixed maturity securities, estimated fair value		1,110,309	485,468
Available-for-sale fixed maturity securities, gross unrealized holding losses		(28,868)	(7,916)
Foreign Governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		419,764	31,752
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(14,461)	(452)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		84,776	63,406
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(7,117)	(1,958)
Available-for-sale fixed maturity securities, estimated fair value		504,540	95,158
Available-for-sale fixed maturity securities, gross unrealized holding losses		(21,578)	(2,410)
Commercial Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		653,410	253,936
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(10,128)	(1,980)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		709,971	481,216
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(34,399)	(14,579)
Available-for-sale fixed maturity securities, estimated fair value		1,363,381	735,152
Available-for-sale fixed maturity securities, gross unrealized holding losses		(44,527)	(16,559)
Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		276,777	157,508
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(3,685)	(1,345)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		242,949	148,960
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(8,814)	(3,518)
Available-for-sale fixed maturity securities, estimated fair value		519,726	306,468
Available-for-sale fixed maturity securities, gross unrealized holding losses		(12,499)	(4,863)
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		1,645	14,263
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(11)	(123)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		17,030	15,165
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(202)	(99)
Available-for-sale fixed maturity securities, estimated fair value		18,675	29,428
Available-for-sale fixed maturity securities, gross unrealized holding losses		(213)	(222)
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		313,164	149,345
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(10,965)	(863)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		222,761	187,754
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(6,499)	(1,874)
Available-for-sale fixed maturity securities, estimated fair value		535,925	337,099
Available-for-sale fixed maturity securities, gross unrealized holding losses		(17,464)	(2,737)
Total Fixed Maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		2,413,109	777,807
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(53,711)	(6,290)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		1,983,912	1,468,807
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		(77,504)	(31,054)
Available-for-sale fixed maturity securities, estimated fair value		4,397,021	2,246,614
Available-for-sale fixed maturity securities, gross unrealized holding losses		(131,215)	(37,344)
Insurance, Banks And Other Financial Institutions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	[1]		60,848
Available-for-sale securities, gross unrealized holding losses, less than 12 months	[1]		(4,843)
Available-for-sale securities, estimated fair value, 12 months or longer	[1]		1,291
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	[1]		(610)
Available-for-sale securities, estimated fair value	[1]		62,139
Available-for-sale securities, gross unrealized holding losses	[1]		(5,453)
Industrial, Consumer And All Other [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	[1]		78,552
Available-for-sale securities, gross unrealized holding losses, less than 12 months	[1]		(11,798)
Available-for-sale securities, estimated fair value, 12 months or longer	[1]		11,243
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	[1]		(2,684)
Available-for-sale securities, estimated fair value	[1]		89,795
Available-for-sale securities, gross unrealized holding losses	[1]		(14,482)
Total Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	[1]		139,400
Available-for-sale securities, gross unrealized holding losses, less than 12 months	[1]		(16,641)
Available-for-sale securities, estimated fair value, 12 months or longer	[1]		12,534
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	[1]		(3,294)
Available-for-sale securities, estimated fair value	[1]		151,934
Available-for-sale securities, gross unrealized holding losses	[1]		(19,935)
Short-Term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months		197,643	369,104
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months		(2,774)	(69)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer		0	0
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer		0	0
Available-for-sale fixed maturity securities, estimated fair value		197,643	369,104
Available-for-sale fixed maturity securities, gross unrealized holding losses		$ (2,774)	$ (69)

[1] Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale. Prior periods have not been restated to conform to the current presentation. See note 1.