Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Market Value, Total	$ 2,429,993	$ 1,540,376
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(243,767)	(45,484)
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	2,075,489	759,174
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(159,937)	(8,539)
Available for sale securities, Greater than 12 months, Market Value	354,504	781,202
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(83,830)	(36,945)
Available-for-sale Securities, Market Value, Total	2,429,993	1,540,376
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(243,767)	(45,484)
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	102,257	34,542
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(3,625)	(1,067)
Available for sale securities, Greater than 12 months, Market Value	56,571	188,755
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(7,462)	(6,411)
Available-for-sale Securities, Market Value, Total	158,828	223,297
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(11,087)	(7,478)
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	692,049	226,521
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(35,783)	(2,554)
Available for sale securities, Greater than 12 months, Market Value	130,311	357,728
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(16,942)	(11,562)
Available-for-sale Securities, Market Value, Total	822,360	584,249
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(52,725)	(14,116)
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	491,144	251,967
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(38,231)	(3,292)
Available for sale securities, Greater than 12 months, Market Value	8,969	43,129
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(1,254)	(6,785)
Available-for-sale Securities, Market Value, Total	500,113	295,096
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(39,485)	(10,077)
Due After Ten Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	151,590	54,347
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(12,185)	(570)
Available for sale securities, Greater than 12 months, Market Value	34,620	81,028
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(50,041)	(11,460)
Available-for-sale Securities, Market Value, Total	186,210	135,375
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(62,226)	(12,030)
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	603,807	159,695
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(68,849)	(887)
Available for sale securities, Greater than 12 months, Market Value	107,550	76,351
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(7,825)	(422)
Available-for-sale Securities, Market Value, Total	711,357	236,046
Available-for-sale Securities, Gross Unrealized Depreciation, Total	(76,674)	(1,309)
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less than 12 months, Market Value	34,642	32,102
Available for sale securities, Less than 12 months, Gross Unrealized Depreciation	(1,264)	(169)
Available for sale securities, Greater than 12 months, Market Value	16,483	34,211
Available for sale securities, Greater than 12 months, Gross Unrealized Depreciation	(306)	(305)
Available-for-sale Securities, Market Value, Total	51,125	66,313
Available-for-sale Securities, Gross Unrealized Depreciation, Total	$ (1,570)	$ (474)