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Schedule I - Summary of Investments - Other Than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Amortized Cost or Cost	$ 9,071,424
Carrying Amount	8,693,729
Short-term Investments [Member]
Amortized Cost or Cost	309,300
Carrying Amount	309,317
Other Investments [Member]
Amortized Cost or Cost	91,164
Carrying Amount	91,164
Alternative Investments [Member]
Amortized Cost or Cost	395,779
Carrying Amount	395,779
Held-to-maturity Securities [Member] | All other corporate securities
Amortized Cost or Cost	22,700
Fair Value	21,923
Carrying Amount	22,700
Held-to-maturity Securities [Member] | Fixed Income Securities [Member]
Amortized Cost or Cost	22,700
Fair Value	21,923
Carrying Amount	22,700
AFS Fixed Income Securities [Member] | US Government Agencies Debt Securities [Member]
Amortized Cost or Cost	223,157
Fair Value	205,035
Carrying Amount	205,035
AFS Fixed Income Securities [Member] | Foreign Government
Amortized Cost or Cost	11,140
Fair Value	9,803
Carrying Amount	9,803
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
Amortized Cost or Cost	612,938
Fair Value	585,965
Carrying Amount	585,965
AFS Fixed Income Securities [Member] | Public Utilities
Amortized Cost or Cost	150,064
Fair Value	142,425
Carrying Amount	142,425
AFS Fixed Income Securities [Member] | All other corporate securities
Amortized Cost or Cost	2,683,984
Fair Value	2,568,814
Carrying Amount	2,568,814
AFS Fixed Income Securities [Member] | CLO and Other ABS
Amortized Cost or Cost	1,911,831
Fair Value	1,834,827
Carrying Amount	1,834,827
AFS Fixed Income Securities [Member] | Commercial Mortgage-backed Securities (CMBS) [Member]
Amortized Cost or Cost	1,568,960
Fair Value	1,477,483
Carrying Amount	1,477,483
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
Amortized Cost or Cost	718,623
Fair Value	674,845
Carrying Amount	674,845
AFS Fixed Income Securities [Member] | Fixed Income Securities [Member]
Amortized Cost or Cost	7,880,697
Fair Value	7,499,197
Carrying Amount	7,499,197
Equity Securities [Member] | Banks, trusts, and insurance companies
Amortized Cost or Cost	33,224
Fair Value	32,725
Carrying Amount	32,725
Equity Securities [Member] | Industrial, miscellaneous and all other
Amortized Cost or Cost	147,892
Fair Value	152,614
Carrying Amount	152,614
Equity Securities [Member] | Preferred Stock [Member]
Amortized Cost or Cost	1,960
Fair Value	1,816
Carrying Amount	1,816
Equity Securities [Member] | Equity Securities [Member]
Amortized Cost or Cost	183,076
Fair Value	187,155
Carrying Amount	187,155
Commercial Mortgage Loans [Member]
Amortized Cost or Cost	188,708
Carrying Amount	$ 188,417

X

- Definition

Amount of investment held by insurance company, excluding investment in related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15(Column D))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-7

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- Definition

Cost of investment held by insurance company, excluding investment in related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15(Column B))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-7

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15(Column C))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-7

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