Schedule I - Summary of Investments - Other Than Investments In Related Parties (Details) $ in Thousands	Dec. 31, 2023 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	$ 4,579,796
Fair Value	4,349,781
Amount Which is Presented in the Balance Sheet	4,349,781
U.S. Government or government agencies and authorities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	292,380
Fair Value	274,973
Amount Which is Presented in the Balance Sheet	274,973
States, municipalities and political subdivisions
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	482,367
Fair Value	454,381
Amount Which is Presented in the Balance Sheet	454,381
Foreign governments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	26,476
Fair Value	25,471
Amount Which is Presented in the Balance Sheet	25,471
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	82,837
Fair Value	76,720
Amount Which is Presented in the Balance Sheet	76,720
All other corporate bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	1,809,650
Fair Value	1,683,983
Amount Which is Presented in the Balance Sheet	1,683,983
Asset-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	1,113,459
Fair Value	1,026,393
Amount Which is Presented in the Balance Sheet	1,026,393
Total Fixed Maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	3,807,169
Fair Value	3,541,921
Amount Which is Presented in the Balance Sheet	3,541,921
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	604
Fair Value	543
Amount Which is Presented in the Balance Sheet	543
Banks, trusts and insurance companies
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	15,104
Fair Value	12,042
Amount Which is Presented in the Balance Sheet	12,042
Industrial, miscellaneous and all other
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	148,554
Fair Value	138,710
Amount Which is Presented in the Balance Sheet	138,710
Equities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	164,262
Fair Value	151,295
Amount Which is Presented in the Balance Sheet	151,295
Other long-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	372,580
Fair Value	420,780
Amount Which is Presented in the Balance Sheet	420,780
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	235,785
Fair Value	235,785
Amount Which is Presented in the Balance Sheet	$ 235,785