Schedule I: Summary of Investments—Other Than Investments in Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	$ 6,720,912
Fair Value	6,289,347
Amount Reflected on the Consolidated Balance Sheet	6,289,347
Loaned securities	203,693	$ 112,139
Reinvested cash collateral held under securities lending agreements	149,364	$ 99,735
Loaned securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Loaned securities	127,000
U.S. government and agency securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	171,194
Fair Value	144,396
Amount Reflected on the Consolidated Balance Sheet	144,396
State and municipal obligations
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	158,539
Fair Value	142,785
Amount Reflected on the Consolidated Balance Sheet	142,785
Corporate bonds and notes
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	2,876,175
Fair Value	2,629,284
Amount Reflected on the Consolidated Balance Sheet	2,629,284
RMBS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	1,089,919
Fair Value	1,014,071
Amount Reflected on the Consolidated Balance Sheet	1,014,071
CMBS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	605,029
Fair Value	558,383
Amount Reflected on the Consolidated Balance Sheet	558,383
CLO
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	494,339
Fair Value	487,849
Amount Reflected on the Consolidated Balance Sheet	487,849
Other ABS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	286,988
Fair Value	284,559
Amount Reflected on the Consolidated Balance Sheet	284,559
Foreign government and agency securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	5,128
Fair Value	5,087
Amount Reflected on the Consolidated Balance Sheet	5,087
Mortgage insurance-linked notes
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	47,456
Fair Value	48,996
Amount Reflected on the Consolidated Balance Sheet	48,996
Total fixed-maturities available for sale
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	5,734,767
Fair Value	5,315,410
Amount Reflected on the Consolidated Balance Sheet	5,315,410
Trading securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	110,484
Fair Value	106,423
Amount Reflected on the Consolidated Balance Sheet	106,423
Reinvested cash collateral held under securities lending agreements	149,000
Common stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	173,925
Fair Value	164,955
Amount Reflected on the Consolidated Balance Sheet	164,955
Total equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	173,925
Fair Value	164,955
Amount Reflected on the Consolidated Balance Sheet	164,955
Mortgage loans held for sale
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	32,132
Fair Value	32,755
Amount Reflected on the Consolidated Balance Sheet	32,755
Other invested assets
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	8,461
Fair Value	8,625
Amount Reflected on the Consolidated Balance Sheet	8,625
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	661,143
Fair Value	661,179
Amount Reflected on the Consolidated Balance Sheet	661,179
Short-term investments | Loaned securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Loaned securities	1,000
Equity securities | Loaned securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Loaned securities	$ 76,000