Fair Value (Fair Value Measurement Levels For All Assets, Recorded At Fair And Market Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	$ 6,824,459	$ 6,962,075
Fixed maturities - available for sale, at fair value	2,350	2,337
Equity securities, at fair value	724,325	564,338
Other invested assets, at fair value	1,767,963	1,717,336
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Fixed maturities - available for sale, at fair value
Equity securities, at fair value	693,303	540,894
Other invested assets, at fair value
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	6,449,983	6,578,081
Equity securities, at fair value	31,022	23,444
Other invested assets, at fair value
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	374,476	383,994
Fixed maturities - available for sale, at fair value	2,350	2,337
Equity securities, at fair value
Other invested assets, at fair value	1,767,963	1,717,336
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	929,625	2,242,797
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	929,625	2,242,797
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
U.S. States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	503,854	499,089
U.S. States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
U.S. States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	503,854	499,089
U.S. States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	2,598,487	2,216,153
Corporate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Corporate Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	2,231,309	1,839,903
Corporate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	367,178	376,250
Asset-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	411,061	221,255
Asset-backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Asset-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	411,061	221,255
Asset-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	229,368	136,604
Commercial [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Commercial [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	229,368	136,604
Commercial [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Agency Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	600,878	148,774
Agency Residential [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Agency Residential [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	600,878	148,774
Agency Residential [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Non-agency Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	3,110	3,114
Non-agency Residential [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Non-agency Residential [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	3,110	3,114
Non-agency Residential [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Foreign Government Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	539,792	579,586
Foreign Government Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Foreign Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	539,792	579,586
Foreign Government Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Foreign Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	1,008,284	914,703
Foreign Corporate Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Foreign Corporate Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	1,000,986	906,959
Foreign Corporate Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	$ 7,298	$ 7,744