SCHEDULE I - SUMMARY OF INVESTMENTS - OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) $ in Thousands	Dec. 31, 2024 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	$ 6,194,269
Fair Value	5,866,451
Amount at which shown in the balance sheet	5,866,451
Fixed income
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	6,178,123
Fair Value	5,851,689
Amount at which shown in the balance sheet	5,851,689
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	265,349
Fair Value	260,493
Amount at which shown in the balance sheet	260,493
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	2,065,953
Fair Value	1,875,495
Amount at which shown in the balance sheet	1,875,495
Fixed income | Foreign government debt
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	4,487
Fair Value	3,798
Amount at which shown in the balance sheet	3,798
Fixed income | Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	229,398
Fair Value	229,258
Amount at which shown in the balance sheet	229,258
Fixed income | ABS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	155,594
Fair Value	156,517
Amount at which shown in the balance sheet	156,517
Fixed income | CLOs
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	199,773
Fair Value	200,059
Amount at which shown in the balance sheet	200,059
Fixed income | Mortgage-backed
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	617,325
Fair Value	585,931
Amount at which shown in the balance sheet	585,931
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	2,628,229
Fair Value	2,528,123
Amount at which shown in the balance sheet	2,528,123
Fixed income | Commercial paper
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	12,015
Fair Value	12,015
Amount at which shown in the balance sheet	12,015
Equity Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	16,146
Fair Value	14,762
Amount at which shown in the balance sheet	14,762
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	16,146
Fair Value	14,762
Amount at which shown in the balance sheet	$ 14,762