Fair Value (Fair Value Measurement Levels For All Assets And Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	$ 17,055,259	$ 16,824,944
Fixed maturities, fair value	4,431	5,826
Equity securities, fair value	949,170	931,457
Equity index put option contracts	9,088	5,584
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, fair value
Equity securities, fair value	875,708	864,584
Equity index put option contracts
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, fair value
Equity securities, fair value	63,585	66,873
Equity index put option contracts
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, fair value	4,431	5,826
Equity securities, fair value	9,877
Equity index put option contracts	9,088	5,584
Fixed Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	17,055,259	16,824,944
Fixed Maturity Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value
Fixed Maturity Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	16,031,421	16,051,965
Fixed Maturity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	1,023,838	772,979
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 maturities, market value	1,434,931	1,515,803
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 maturities, 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 maturities, market value	1,434,931	1,515,803
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 maturities, market value
Obligations Of U.S. States And Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	532,281	536,915
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 maturities, 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 maturities, market value	532,281	536,915
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 maturities, market value
Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	6,617,788	6,374,946
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 maturities, market value
Corporate Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	5,895,954	5,757,358
Corporate Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	721,834	617,588
Asset-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	1,069,558	897,333
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 maturities, market value
Asset-Backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	773,828	743,692
Asset-Backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	295,730	153,641
Commercial Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	919,796	844,557
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 maturities, 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 maturities, market value	919,796	844,557
Commercial Mortgage-Backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value
Agency Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	2,089,251	2,198,581
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 maturities, market value
Agency Residential [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	2,089,251	2,198,581
Agency Residential [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value
Non-Agency Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	3,111	5,703
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 maturities, market value
Non-Agency Residential [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	3,111	5,703
Non-Agency Residential [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value
Foreign Government Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	1,501,200	1,505,950
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 maturities, market value
Foreign Government Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	1,501,200	1,505,950
Foreign Government Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value
Foreign Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	2,887,343	2,945,156
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 maturities, market value
Foreign Corporate Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	2,881,069	2,943,406
Foreign Corporate Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, market value	$ 6,274	$ 1,750