Fair Value (Fair Value Measurement Levels For All Assets, Recorded At Fair And Market Value)(Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	$ 6,206,415	$ 5,970,496
Equity securities - available for sale, at fair value	852,993	887,800
Other invested assets, at fair value	1,837,302	1,766,626
Quoted Prices in Active Markets For Identical Assets Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Equity securities - available for sale, at fair value	835,536	827,237
Other invested assets, at fair value
Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	6,119,291	5,902,761
Equity securities - available for sale, at fair value	17,457	60,563
Other invested assets, at fair value
Significant Unobservable Inputs Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	87,124	67,735
Equity securities - available for sale, at fair value
Other invested assets, at fair value	1,837,302	1,766,626
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	771,220	691,080
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member] | Quoted Prices in Active Markets For Identical Assets 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] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	771,220	691,080
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Obligations of U.S. States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	712,437	729,984
Obligations of U.S. States and Political Subdivisions [Member] | Quoted Prices in Active Markets For Identical Assets Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Obligations of U.S. States and Political Subdivisions [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	712,437	729,984
Obligations of U.S. States and Political Subdivisions [Member] | Significant Unobservable 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	2,271,618	2,154,203
Corporate Securities [Member] | Quoted Prices in Active Markets For Identical Assets 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] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	2,187,296	2,089,006
Corporate Securities [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	84,322	65,197
Asset-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	176,170	137,027
Asset-backed Securities [Member] | Quoted Prices in Active Markets For Identical Assets 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] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	176,170	137,027
Asset-backed Securities [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Commercial Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	75,622	75,493
Commercial Mortgage-Backed Securities [Member] | Quoted Prices in Active Markets For Identical Assets Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value
Commercial Mortgage-Backed Securities [Member] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	75,622	75,493
Commercial Mortgage-Backed Securities [Member] | Significant Unobservable 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	698,466	715,144
Agency Residential [Member] | Quoted Prices in Active Markets For Identical Assets 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] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	698,466	715,144
Agency Residential [Member] | Significant Unobservable 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	79	88
Non-agency Residential [Member] | Quoted Prices in Active Markets For Identical Assets 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] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	79	88
Non-agency Residential [Member] | Significant Unobservable 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	489,095	507,277
Foreign Government Securities [Member] | Quoted Prices in Active Markets For Identical Assets 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] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	489,095	507,277
Foreign Government Securities [Member] | Significant Unobservable 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	1,011,708	960,200
Foreign Corporate Securities [Member] | Quoted Prices in Active Markets For Identical Assets 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] | Significant Other Observable Inputs Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	1,008,906	957,662
Foreign Corporate Securities [Member] | Significant Unobservable Inputs Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities - available for sale, at market value	$ 2,802	$ 2,538