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]
Fair value	$ 13,867,405
Amount shown on the balance sheet	14,353,284
Fixed maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	12,176,473
Fair value	11,326,894
Amount shown on the balance sheet	11,326,894
Fixed maturities | U.S. government and agency
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	2,731,733
Fair value	2,639,330
Amount shown on the balance sheet	2,639,330
Fixed maturities | Non-U.S. government
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	612,546
Fair value	562,029
Amount shown on the balance sheet	562,029
Fixed maturities | Corporate debt
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	4,680,798
Fair value	4,255,556
Amount shown on the balance sheet	4,255,556
Fixed maturities | Agency RMBS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	1,297,423
Fair value	1,202,785
Amount shown on the balance sheet	1,202,785
Fixed maturities | CMBS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	1,029,863
Fair value	947,778
Amount shown on the balance sheet	947,778
Fixed maturities | Non-agency RMBS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	151,907
Fair value	133,534
Amount shown on the balance sheet	133,534
Fixed maturities | ABS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	1,499,728
Fair value	1,429,527
Amount shown on the balance sheet	1,429,527
Fixed maturities | Municipals
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	172,475
Fair value	156,355
Amount shown on the balance sheet	156,355
Fixed maturities, held to maturity, at amortized cost
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	698,351
Fair value	674,743
Amount shown on the balance sheet	698,351
Fixed maturities, held to maturity, at amortized cost | Corporate debt
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	85,200
Fair value	73,772
Amount shown on the balance sheet	85,200
Fixed maturities, held to maturity, at amortized cost | ABS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized cost	613,151
Fair value	600,971
Amount shown on the balance sheet	613,151
Mortgage loans
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair value	627,437
Amount shown on the balance sheet	627,437
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair value	70,310
Amount shown on the balance sheet	70,310
Equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair value	485,253
Amount shown on the balance sheet	485,253
Other investments, at fair value
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair value	682,768
Amount shown on the balance sheet	996,751
Equity method investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Fair value	0
Amount shown on the balance sheet	$ 148,288