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Schedule I - Summary of Investments - Other Than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Amortized Cost or Cost	$ 8,045,330
Carrying Amount	7,837,469
Short-term Investments [Member]
Amortized Cost or Cost	440,439
Carrying Amount	440,456
Other Investments [Member]
Amortized Cost or Cost	71,244
Carrying Amount	71,244
Alternative Investments [Member]
Amortized Cost or Cost	371,316
Carrying Amount	371,316
Held-to-maturity Securities [Member] | Obligations of States and Political Subdivisions [Member]
Amortized Cost or Cost	3,405
Fair Value	3,405
Carrying Amount	3,405
Held-to-maturity Securities [Member] | Public Utilities
Amortized Cost or Cost	0
Fair Value	0
Carrying Amount	0
Held-to-maturity Securities [Member] | All other corporate securities
Amortized Cost or Cost	27,752
Fair Value	26,432
Carrying Amount	27,752
Held-to-maturity Securities [Member] | Fixed Income Securities [Member]
Amortized Cost or Cost	31,157
Fair Value	29,837
Carrying Amount	31,157
AFS Fixed Income Securities [Member] | US Government Agencies Debt Securities [Member]
Amortized Cost or Cost	209,528
Fair Value	189,239
Carrying Amount	189,239
AFS Fixed Income Securities [Member] | Foreign Government
Amortized Cost or Cost	11,199
Fair Value	9,608
Carrying Amount	9,608
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
Amortized Cost or Cost	965,231
Fair Value	918,018
Carrying Amount	918,018
AFS Fixed Income Securities [Member] | Public Utilities
Amortized Cost or Cost	110,544
Fair Value	97,717
Carrying Amount	97,717
AFS Fixed Income Securities [Member] | All other corporate securities
Amortized Cost or Cost	2,448,111
Fair Value	2,237,308
Carrying Amount	2,237,308
AFS Fixed Income Securities [Member] | CLO and Other ABS
Amortized Cost or Cost	1,607,660
Fair Value	1,485,973
Carrying Amount	1,485,973
AFS Fixed Income Securities [Member] | Commercial Mortgage-backed Securities (CMBS) [Member]
Amortized Cost or Cost	1,169,546
Fair Value	1,059,832
Carrying Amount	1,059,832
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
Amortized Cost or Cost	663,935
Fair Value	614,412
Carrying Amount	614,412
AFS Fixed Income Securities [Member] | Fixed Income Securities [Member]
Amortized Cost or Cost	7,185,754
Fair Value	6,612,107
Carrying Amount	6,612,107
Equity Securities [Member] | Banks, trusts, and insurance companies
Amortized Cost or Cost	22,579
Fair Value	20,201
Carrying Amount	20,201
Equity Securities [Member] | Industrial, miscellaneous and all other
Amortized Cost or Cost	142,892
Fair Value	140,154
Carrying Amount	140,154
Equity Securities [Member] | Preferred Stock [Member]
Amortized Cost or Cost	1,960
Fair Value	1,645
Carrying Amount	1,645
Equity Securities [Member] | Equity Securities [Member]
Amortized Cost or Cost	167,431
Fair Value	162,000
Carrying Amount	162,000
Commercial Mortgage Loans [Member]
Amortized Cost or Cost	149,305
Carrying Amount	$ 149,189

X

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15(Column D))
-URI https://asc.fasb.org/extlink&oid=122147990&loc=d3e611379-123010

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15(Column B))
-URI https://asc.fasb.org/extlink&oid=122147990&loc=d3e611379-123010

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+ References

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