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Schedule I - Summary of Investments - Other Than Investments in Related Parties (Details) $ in Thousands | Dec. 31, 2021 USD ($)
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Amortized Cost or Cost | $ 7,781,136
Carrying Amount | 8,026,988
Short-term Investments [Member] |
Amortized Cost or Cost | 447,862
Carrying Amount | 447,863
Other Investments [Member] |
Amortized Cost or Cost | 409,032
Carrying Amount | 409,032
Held-to-maturity Securities [Member] | Obligations of States and Political Subdivisions [Member] |
Amortized Cost or Cost | 3,442
Fair Value | 3,576
Carrying Amount | 3,440
Held-to-maturity Securities [Member] | Public Utilities |
Amortized Cost or Cost | 1,345
Fair Value | 1,368
Carrying Amount | 1,352
Held-to-maturity Securities [Member] | All other corporate securities |
Amortized Cost or Cost | 24,067
Fair Value | 24,516
Carrying Amount | 23,993
Held-to-maturity Securities [Member] | Fixed Income Securities [Member] |
Amortized Cost or Cost | 28,854
Fair Value | 29,460
Carrying Amount | 28,785
AFS Fixed Income Securities [Member] | US Government Agencies Debt Securities [Member] |
Amortized Cost or Cost | 127,974
Fair Value | 130,458
Carrying Amount | 130,458
AFS Fixed Income Securities [Member] | Foreign Government |
Amortized Cost or Cost | 15,420
Fair Value | 15,860
Carrying Amount | 15,860
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member] |
Amortized Cost or Cost | 1,121,422
Fair Value | 1,189,308
Carrying Amount | 1,189,308
AFS Fixed Income Securities [Member] | Public Utilities |
Amortized Cost or Cost | 119,980
Fair Value | 122,329
Carrying Amount | 122,329
AFS Fixed Income Securities [Member] | All other corporate securities |
Amortized Cost or Cost | 2,358,369
Fair Value | 2,451,274
Carrying Amount | 2,451,274
AFS Fixed Income Securities [Member] | CLO and Other ABS |
Amortized Cost or Cost | 1,343,687
Fair Value | 1,350,814
Carrying Amount | 1,350,814
AFS Fixed Income Securities [Member] | Commercial Mortgage-backed Securities (CMBS) [Member] |
Amortized Cost or Cost | 756,280
Fair Value | 776,252
Carrying Amount | 776,252
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member] |
Amortized Cost or Cost | 647,621
Fair Value | 673,681
Carrying Amount | 673,681
AFS Fixed Income Securities [Member] | Fixed Income Securities [Member] |
Amortized Cost or Cost | 6,490,753
Fair Value | 6,709,976
Carrying Amount | 6,709,976
Equity Securities [Member] | Banks, trusts, and insurance companies |
Amortized Cost or Cost | 45,537
Fair Value | 44,086
Carrying Amount | 44,086
Equity Securities [Member] | Industrial, miscellaneous and all other |
Amortized Cost or Cost | 261,343
Fair Value | 289,363
Carrying Amount | 289,363
Equity Securities [Member] | Preferred Stock [Member] |
Amortized Cost or Cost | 1,960
Fair Value | 2,088
Carrying Amount | 2,088
Equity Securities [Member] | Equity Securities [Member] |
Amortized Cost or Cost | 308,840
Fair Value | 335,537
Carrying Amount | 335,537
Commercial Mortgage Loans [Member] |
Amortized Cost or Cost | 95,795
Carrying Amount | $ 95,795

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