SCHEDULE I - SUMMARY OF INVESTMENTS - OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) $ in Thousands	Dec. 31, 2025 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	$ 5,960,287
Fair Value	5,806,553
Amount at which shown in the balance sheet	5,806,553
Fixed income
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	5,944,001
Fair Value	5,791,231
Amount at which shown in the balance sheet	5,791,231
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	279,359
Fair Value	277,812
Amount at which shown in the balance sheet	277,812
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	1,961,841
Fair Value	1,838,764
Amount at which shown in the balance sheet	1,838,764
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	4,067
Amount at which shown in the balance sheet	4,067
Fixed income | Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	233,134
Fair Value	348,387
Amount at which shown in the balance sheet	348,387
Fixed income | ABS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	225,478
Fair Value	226,561
Amount at which shown in the balance sheet	226,561
Fixed income | CLOs
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	99,182
Fair Value	99,287
Amount at which shown in the balance sheet	99,287
Fixed income | Mortgage-backed
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	604,645
Fair Value	596,807
Amount at which shown in the balance sheet	596,807
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	2,479,214
Fair Value	2,342,885
Amount at which shown in the balance sheet	2,342,885
Fixed income | Commercial paper
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	56,661
Fair Value	56,661
Amount at which shown in the balance sheet	56,661
Equity Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	16,286
Fair Value	15,322
Amount at which shown in the balance sheet	15,322
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	16,286
Fair Value	15,322
Amount at which shown in the balance sheet	$ 15,322