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Schedule I - Summary of Investments - Other Than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2021 USD ($)
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

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 http://asc.fasb.org/extlink&oid=122147990&loc=d3e611379-123010

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

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