SCHEDULE I - Consolidated Summary of Investments Other Than Investments in Related Parties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fair Value	$ 15,019,603
Amount at which shown in the balance sheet	15,019,603
[FixedMaturitiesMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	13,394,404
Fair Value	13,941,829
Amount at which shown in the balance sheet	13,941,829
[FixedMaturitiesMember] | [USTreasuryAndGovernmentMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,084,533
Fair Value	1,115,777
Amount at which shown in the balance sheet	1,115,777
[FixedMaturitiesMember] | [USStatesAndPoliticalSubdivisionsMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	117,528
Fair Value	123,684
Amount at which shown in the balance sheet	123,684
[FixedMaturitiesMember] | [NonUsSovereignGovernmentSupranationalAndGovernmentRelatedMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,807,363
Fair Value	2,964,091
Amount at which shown in the balance sheet	2,964,091
[FixedMaturitiesMember] | [CorporateDebtSecuritiesMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5,461,478
Fair Value	5,746,997
Amount at which shown in the balance sheet	5,746,997
[FixedMaturitiesMember] | [AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	626,508
Fair Value	633,799
Amount at which shown in the balance sheet	633,799
[FixedMaturitiesMember] | [ResidentialMortgageBackedSecuritiesMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	3,224,850
Fair Value	3,282,901
Amount at which shown in the balance sheet	3,282,901
[FixedMaturitiesMember] | [CommercialMortgageBackedSecuritiesMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	72,144
Fair Value	74,580
Amount at which shown in the balance sheet	74,580
[EquitySecuritiesMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	917,613
Fair Value	944,691
Amount at which shown in the balance sheet	944,691
[EquitySecuritiesMember] | [BanksTrustAndInsuranceEquitiesMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	151,622
Fair Value	137,600
Amount at which shown in the balance sheet	137,600
[EquitySecuritiesMember] | [PublicUtilityEquitiesMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	25,822
Fair Value	28,415
Amount at which shown in the balance sheet	28,415
[EquitySecuritiesMember] | [IndustrialMiscellaneousAndAllOthersMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	740,169
Fair Value	778,676
Amount at which shown in the balance sheet	778,676
[ShortTermInvestmentsMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	42,563
Fair Value	42,571
Amount at which shown in the balance sheet	42,571
[OtherInvestedAssetsMember]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fair Value	90,512
Amount at which shown in the balance sheet	$ 90,512