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Schedule I - Summary of Investments - Other Than Investments in Related Parties (Details) $ in Thousands | Dec. 31, 2019 USD ($)
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Amortized Cost or Cost | $ 6,472,113
Carrying Amount | 6,688,654
Short-term Investments [Member] |
Amortized Cost or Cost | 282,490
Fair Value | 282,490
Carrying Amount | 282,490
Other Investments [Member] |
Amortized Cost or Cost | 216,807
Carrying Amount | 216,807
Held-to-maturity Securities [Member] | Obligations of States and Political Subdivisions [Member] |
Amortized Cost or Cost | 4,573
Fair Value | 4,921
Carrying Amount | 4,580
Held-to-maturity Securities [Member] | Public Utilities |
Amortized Cost or Cost | 3,608
Fair Value | 3,967
Carrying Amount | 3,673
Held-to-maturity Securities [Member] | All other corporate securities |
Amortized Cost or Cost | 12,588
Fair Value | 13,087
Carrying Amount | 12,547
Held-to-maturity Securities [Member] | Fixed Income Securities [Member] |
Amortized Cost or Cost | 20,769
Fair Value | 21,975
Carrying Amount | 20,800
AFS Fixed Income Securities [Member] | US Government Agencies Debt Securities [Member] |
Amortized Cost or Cost | 112,680
Fair Value | 116,186
Carrying Amount | 116,186
AFS Fixed Income Securities [Member] | Foreign Government |
Amortized Cost or Cost | 18,011
Fair Value | 18,542
Carrying Amount | 18,542
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member] |
Amortized Cost or Cost | 1,168,185
Fair Value | 1,230,090
Carrying Amount | 1,230,090
AFS Fixed Income Securities [Member] | Public Utilities |
Amortized Cost or Cost | 35,679
Fair Value | 37,084
Carrying Amount | 37,084
AFS Fixed Income Securities [Member] | All other corporate securities |
Amortized Cost or Cost | 1,831,202
Fair Value | 1,910,393
Carrying Amount | 1,910,393
AFS Fixed Income Securities [Member] | CLO and Other ABS |
Amortized Cost or Cost | 790,517
Fair Value | 793,012
Carrying Amount | 793,012
AFS Fixed Income Securities [Member] | Commercial Mortgage-backed Securities (CMBS) [Member] |
Amortized Cost or Cost | 514,709
Fair Value | 538,344
Carrying Amount | 538,344
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member] |
Amortized Cost or Cost | 1,409,003
Fair Value | 1,451,969
Carrying Amount | 1,451,969
AFS Fixed Income Securities [Member] | Fixed Income Securities [Member] |
Amortized Cost or Cost | 5,879,986
Fair Value | 6,095,620
Carrying Amount | 6,095,620
Equity Securities [Member] | Banks, trusts, and insurance companies |
Amortized Cost or Cost | 17,357
Fair Value | 17,368
Carrying Amount | 17,368
Equity Securities [Member] | Industrial, miscellaneous and all other |
Amortized Cost or Cost | 51,815
Fair Value | 52,532
Carrying Amount | 52,532
Equity Securities [Member] | Preferred Stock [Member] |
Amortized Cost or Cost | 2,889
Fair Value | 3,037
Carrying Amount | 3,037
Equity Securities [Member] | Equity Securities [Member] |
Amortized Cost or Cost | 72,061
Fair Value | 72,937
Carrying Amount | $ 72,937

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