Schedule I - Summary of Investments - Other Than Investments In Related Parties (Details) $ in Thousands	Dec. 31, 2022 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	$ 4,756,673
Fair Value	4,387,683
Amount Which is Presented in the Balance Sheet	4,387,683
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	284,759
Fair Value	260,113
Amount Which is Presented in the Balance Sheet	260,113
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	483,584
Fair Value	439,450
Amount Which is Presented in the Balance Sheet	439,450
Foreign governments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	31,259
Fair Value	29,597
Amount Which is Presented in the Balance Sheet	29,597
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	98,891
Fair Value	90,106
Amount Which is Presented in the Balance Sheet	90,106
All other corporate bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	1,876,190
Fair Value	1,686,524
Amount Which is Presented in the Balance Sheet	1,686,524
Asset-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	1,122,777
Fair Value	1,010,116
Amount Which is Presented in the Balance Sheet	1,010,116
Total Fixed Maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	3,897,460
Fair Value	3,515,906
Amount Which is Presented in the Balance Sheet	3,515,906
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	527
Amount Which is Presented in the Balance Sheet	527
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	15,813
Fair Value	12,372
Amount Which is Presented in the Balance Sheet	12,372
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	146,012
Fair Value	130,839
Amount Which is Presented in the Balance Sheet	130,839
Equities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	162,429
Fair Value	143,738
Amount Which is Presented in the Balance Sheet	143,738
Other long-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	451,269
Fair Value	482,726
Amount Which is Presented in the Balance Sheet	482,726
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	245,515
Fair Value	245,313
Amount Which is Presented in the Balance Sheet	$ 245,313