Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Contractual Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Market Value, Total	$ 1,682,212	$ 3,470,834
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(48,271)	(130,602)
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	587,262	2,663,097
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(9,667)	(105,810)
Available for sale securities, Greater than 12 months, Market Value	1,094,950	807,737
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(38,604)	(24,792)
Available-for-sale Securities, Market Value, Total	1,682,212	3,470,834
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(48,271)	(130,602)
Due In One Year Or Less [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	37,823	165,545
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(624)	(7,618)
Available for sale securities, Greater than 12 months, Market Value	188,033	118,322
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(9,133)	(1,164)
Available-for-sale Securities, Market Value, Total	225,856	283,867
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(9,757)	(8,782)
Due In One Year Through Five Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	115,774	1,423,431
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(960)	(44,924)
Available for sale securities, Greater than 12 months, Market Value	593,416	525,554
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(15,494)	(9,530)
Available-for-sale Securities, Market Value, Total	709,190	1,948,985
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(16,454)	(54,454)
Due In Five Years Through Ten Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	101,238	624,875
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(6,438)	(35,360)
Available for sale securities, Greater than 12 months, Market Value	95,780	42,902
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(3,859)	(2,773)
Available-for-sale Securities, Market Value, Total	197,018	667,777
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(10,297)	(38,133)
Due After Ten Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	20,475	223,673
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(778)	(14,580)
Available for sale securities, Greater than 12 months, Market Value	109,026	49,260
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(9,591)	(10,178)
Available-for-sale Securities, Market Value, Total	129,501	272,933
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(10,369)	(24,758)
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	295,890	127,052
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(833)	(1,408)
Available for sale securities, Greater than 12 months, Market Value	52,686	47,551
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(102)	(631)
Available-for-sale Securities, Market Value, Total	348,576	174,603
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(935)	(2,039)
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	16,062	98,521
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(34)	(1,920)
Available for sale securities, Greater than 12 months, Market Value	56,009	24,148
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(425)	(516)
Available-for-sale Securities, Market Value, Total	72,071	122,669
Available-for-sale Securities, Gross Unrealized Depreciation, Total	$ (459)	$ (2,436)