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]
Amortized Cost	$ 5,942,709
Fair Value	5,423,838
Amount at which shown in the balance sheet	5,423,838
Fixed income
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	5,926,785
Fair Value	5,409,698
Amount at which shown in the balance sheet	5,409,698
Fixed income | U.S. Treasury securities and obligations of U.S. government corporations and agencies
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	145,581
Fair Value	135,900
Amount at which shown in the balance sheet	135,900
Fixed income | Obligations of U.S. states and political subdivisions
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	2,400,261
Fair Value	2,149,054
Amount at which shown in the balance sheet	2,149,054
Fixed income | Foreign government debt
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	4,486
Fair Value	3,787
Amount at which shown in the balance sheet	3,787
Fixed income | Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	267,319
Fair Value	266,895
Amount at which shown in the balance sheet	266,895
Fixed income | ABS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	126,723
Fair Value	120,687
Amount at which shown in the balance sheet	120,687
Fixed income | CLOs
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	337,656
Fair Value	329,832
Amount at which shown in the balance sheet	329,832
Fixed income | Mortgage-backed
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	481,528
Fair Value	435,224
Amount at which shown in the balance sheet	435,224
Fixed income | All other corporate debt securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	2,149,156
Fair Value	1,954,247
Amount at which shown in the balance sheet	1,954,247
Fixed income | Commercial paper
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	14,075
Fair Value	14,072
Amount at which shown in the balance sheet	14,072
Equity Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	15,924
Fair Value	14,140
Amount at which shown in the balance sheet	14,140
Equity Securities | Industrial, miscellaneous and all other
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	15,924
Fair Value	14,140
Amount at which shown in the balance sheet	$ 14,140