v2.3.0.15
Fair Value Measurements (Summary Of Assets Recorded At Fair Value) (Details) (USD $)
In Thousands
Sep. 30, 2011
Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities$ 4,956,746$ 4,944,507
Equity securities5,2674,631
Estimated Fair Value, Total4,962,0134,949,138
Derivatives, assets46,22964,461
Fair value, total5,008,2425,013,599
Level 1 [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities1,527,5881,875,500
Equity securities5,2674,631
Derivatives, assets00
Fair value, total1,532,8551,880,131
Level 1 [Member] | U.S. Treasury Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities1,155,3281,355,437
Level 1 [Member] | Money Market Funds [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities372,260520,063
Level 1 [Member] | U.S. Government Agencies And FDIC Guaranteed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 1 [Member] | Municipal Debt Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 1 [Member] | Non-U.S. Government Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 1 [Member] | Corporate Debt Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 1 [Member] | Residential Mortgage And Asset-Backed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 1 [Member] | Student Loan-Backed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 2 [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities3,347,3372,988,642
Equity securities00
Derivatives, assets46,22964,461
Fair value, total3,393,5663,053,103
Level 2 [Member] | U.S. Treasury Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 2 [Member] | Money Market Funds [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 2 [Member] | U.S. Government Agencies And FDIC Guaranteed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities1,090,5871,296,110
Level 2 [Member] | Municipal Debt Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities24,59117,625
Level 2 [Member] | Non-U.S. Government Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities211,764278,610
Level 2 [Member] | Corporate Debt Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities1,703,8691,119,254
Level 2 [Member] | Residential Mortgage And Asset-Backed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities316,526277,043
Level 2 [Member] | Student Loan-Backed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 3 [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities81,82180,365
Equity securities00
Derivatives, assets00
Fair value, total81,82180,365
Level 3 [Member] | U.S. Treasury Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 3 [Member] | Money Market Funds [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 3 [Member] | U.S. Government Agencies And FDIC Guaranteed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 3 [Member] | Municipal Debt Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 3 [Member] | Non-U.S. Government Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities25,3149,594
Level 3 [Member] | Corporate Debt Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 3 [Member] | Residential Mortgage And Asset-Backed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities00
Level 3 [Member] | Student Loan-Backed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities56,50770,771
U.S. Treasury Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities1,155,3281,355,437
Money Market Funds [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities372,260520,063
U.S. Government Agencies And FDIC Guaranteed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities1,090,5871,296,110
Municipal Debt Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities24,59117,625
Non-U.S. Government Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities237,078288,204
Corporate Debt Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities1,703,8691,119,254
Residential Mortgage And Asset-Backed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities316,526277,043
Student Loan-Backed Securities [Member]
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Debt securities$ 56,507$ 70,771