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FAIR VALUE MEASUREMENTS - Financial Instruments Measured at Fair Value (Details) - USD ($) $ in Thousands | Mar. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Assets |  |
Fixed maturities, available for sale | $ 11,865,480 | $ 12,152,753
Equity securities | 574,379 | 579,274
Other investments | 938,562 | 930,278
Short-term investments | 91,330 | 223,666
Derivative instruments (refer to Note 5) | 7,309 | 9,439
Total Assets | 13,477,060 | 13,895,410
Liabilities |  |
Derivative instruments (refer to Note 5) | 2,667 | 3,100
Total Liabilities | 2,667 | 3,100
U.S. government and agency |  |
Assets |  |
Fixed maturities, available for sale | 2,553,843 | 2,802,986
Non-U.S. government |  |
Assets |  |
Fixed maturities, available for sale | 714,525 | 729,939
Corporate debt |  |
Assets |  |
Fixed maturities, available for sale | 4,627,610 | 4,842,190
Agency RMBS |  |
Assets |  |
Fixed maturities, available for sale | 1,557,554 | 1,184,845
CMBS |  |
Assets |  |
Fixed maturities, available for sale | 856,108 | 819,608
Non-agency RMBS |  |
Assets |  |
Fixed maturities, available for sale | 189,739 | 122,536
ABS |  |
Assets |  |
Fixed maturities, available for sale | 1,293,874 | 1,539,832
Municipals |  |
Assets |  |
Fixed maturities, available for sale | 72,227 | 110,817
Common stocks |  |
Assets |  |
Equity securities | 2,616 | 2,638
Preferred stocks |  |
Assets |  |
Equity securities | 5,888 | 5,867
Exchange-traded funds |  |
Assets |  |
Equity securities | 314,508 | 314,042
Bond mutual funds |  |
Assets |  |
Equity securities | 251,367 | 256,727
Multi-strategy funds |  |
Assets |  |
Other investments | 16,625 | 24,919
Direct lending funds |  |
Assets |  |
Other investments | 167,425 | 171,048
Private equity funds |  |
Assets |  |
Other investments | 329,542 | 320,690
Real estate funds |  |
Assets |  |
Other investments | 291,564 | 291,640
Other privately held investments |  |
Assets |  |
Other investments | 133,406 | 121,981
Quoted prices in active markets for identical assets (Level 1) |  |
Assets |  |
Fixed maturities, available for sale | 2,518,006 | 2,767,315
Equity securities | 317,127 | 316,683
Other investments | 0 | 0
Short-term investments | 0 | 0
Derivative instruments (refer to Note 5) | 0 | 0
Total Assets | 2,835,133 | 3,083,998
Liabilities |  |
Derivative instruments (refer to Note 5) | 0 | 0
Total Liabilities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | U.S. government and agency |  |
Assets |  |
Fixed maturities, available for sale | 2,518,006 | 2,767,315
Quoted prices in active markets for identical assets (Level 1) | Non-U.S. government |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Corporate debt |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Agency RMBS |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | CMBS |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Non-agency RMBS |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | ABS |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Municipals |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Common stocks |  |
Assets |  |
Equity securities | 2,616 | 2,638
Quoted prices in active markets for identical assets (Level 1) | Preferred stocks |  |
Assets |  |
Equity securities | 3 | 3
Quoted prices in active markets for identical assets (Level 1) | Exchange-traded funds |  |
Assets |  |
Equity securities | 314,508 | 314,042
Quoted prices in active markets for identical assets (Level 1) | Bond mutual funds |  |
Assets |  |
Equity securities | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Multi-strategy funds |  |
Assets |  |
Other investments | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Direct lending funds |  |
Assets |  |
Other investments | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Private equity funds |  |
Assets |  |
Other investments | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Real estate funds |  |
Assets |  |
Other investments | 0 | 0
Quoted prices in active markets for identical assets (Level 1) | Other privately held investments |  |
Assets |  |
Other investments | 0 | 0
Significant other observable inputs (Level 2) |  |
Assets |  |
Fixed maturities, available for sale | 9,180,589 | 9,238,215
Equity securities | 257,252 | 262,591
Other investments | 0 | 0
Short-term investments | 91,330 | 223,666
Derivative instruments (refer to Note 5) | 7,309 | 9,439
Total Assets | 9,536,480 | 9,733,911
Liabilities |  |
Derivative instruments (refer to Note 5) | 2,667 | 3,100
Total Liabilities | 2,667 | 3,100
Significant other observable inputs (Level 2) | U.S. government and agency |  |
Assets |  |
Fixed maturities, available for sale | 35,837 | 35,671
Significant other observable inputs (Level 2) | Non-U.S. government |  |
Assets |  |
Fixed maturities, available for sale | 714,525 | 729,939
Significant other observable inputs (Level 2) | Corporate debt |  |
Assets |  |
Fixed maturities, available for sale | 4,493,868 | 4,715,799
Significant other observable inputs (Level 2) | Agency RMBS |  |
Assets |  |
Fixed maturities, available for sale | 1,557,554 | 1,184,845
Significant other observable inputs (Level 2) | CMBS |  |
Assets |  |
Fixed maturities, available for sale | 856,108 | 819,608
Significant other observable inputs (Level 2) | Non-agency RMBS |  |
Assets |  |
Fixed maturities, available for sale | 189,739 | 122,536
Significant other observable inputs (Level 2) | ABS |  |
Assets |  |
Fixed maturities, available for sale | 1,260,731 | 1,519,000
Significant other observable inputs (Level 2) | Municipals |  |
Assets |  |
Fixed maturities, available for sale | 72,227 | 110,817
Significant other observable inputs (Level 2) | Common stocks |  |
Assets |  |
Equity securities | 0 | 0
Significant other observable inputs (Level 2) | Preferred stocks |  |
Assets |  |
Equity securities | 5,885 | 5,864
Significant other observable inputs (Level 2) | Exchange-traded funds |  |
Assets |  |
Equity securities | 0 | 0
Significant other observable inputs (Level 2) | Bond mutual funds |  |
Assets |  |
Equity securities | 251,367 | 256,727
Significant other observable inputs (Level 2) | Multi-strategy funds |  |
Assets |  |
Other investments | 0 | 0
Significant other observable inputs (Level 2) | Direct lending funds |  |
Assets |  |
Other investments | 0 | 0
Significant other observable inputs (Level 2) | Private equity funds |  |
Assets |  |
Other investments | 0 | 0
Significant other observable inputs (Level 2) | Real estate funds |  |
Assets |  |
Other investments | 0 | 0
Significant other observable inputs (Level 2) | Other privately held investments |  |
Assets |  |
Other investments | 0 | 0
Significant unobservable inputs (Level 3) |  |
Assets |  |
Fixed maturities, available for sale | 166,885 | 147,223
Equity securities | 0 | 0
Other investments | 97,020 | 92,230
Short-term investments | 0 | 0
Derivative instruments (refer to Note 5) | 0 | 0
Total Assets | 263,905 | 239,453
Liabilities |  |
Derivative instruments (refer to Note 5) | 0 | 0
Total Liabilities | 0 | 0
Significant unobservable inputs (Level 3) | U.S. government and agency |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Significant unobservable inputs (Level 3) | Non-U.S. government |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Significant unobservable inputs (Level 3) | Corporate debt |  |
Assets |  |
Fixed maturities, available for sale | 133,742 | 126,391
Significant unobservable inputs (Level 3) | Agency RMBS |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Significant unobservable inputs (Level 3) | CMBS |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Significant unobservable inputs (Level 3) | Non-agency RMBS |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Significant unobservable inputs (Level 3) | ABS |  |
Assets |  |
Fixed maturities, available for sale | 33,143 | 20,832
Significant unobservable inputs (Level 3) | Municipals |  |
Assets |  |
Fixed maturities, available for sale | 0 | 0
Significant unobservable inputs (Level 3) | Common stocks |  |
Assets |  |
Equity securities | 0 | 0
Significant unobservable inputs (Level 3) | Preferred stocks |  |
Assets |  |
Equity securities | 0 | 0
Significant unobservable inputs (Level 3) | Exchange-traded funds |  |
Assets |  |
Equity securities | 0 | 0
Significant unobservable inputs (Level 3) | Bond mutual funds |  |
Assets |  |
Equity securities | 0 | 0
Significant unobservable inputs (Level 3) | Multi-strategy funds |  |
Assets |  |
Other investments | 0 | 0
Significant unobservable inputs (Level 3) | Direct lending funds |  |
Assets |  |
Other investments | 0 | 0
Significant unobservable inputs (Level 3) | Private equity funds |  |
Assets |  |
Other investments | 0 | 0
Significant unobservable inputs (Level 3) | Real estate funds |  |
Assets |  |
Other investments | 0 | 0
Significant unobservable inputs (Level 3) | Other privately held investments |  |
Assets |  |
Other investments | 97,020 | 92,230
Fair value based on NAV practical expedient |  |
Assets |  |
Other investments | 841,542 | 838,048
Total Assets | 841,542 | 838,048
Fair value based on NAV practical expedient | Multi-strategy funds |  |
Assets |  |
Other investments | 16,625 | 24,919
Fair value based on NAV practical expedient | Direct lending funds |  |
Assets |  |
Other investments | 167,425 | 171,048
Fair value based on NAV practical expedient | Private equity funds |  |
Assets |  |
Other investments | 329,542 | 320,690
Fair value based on NAV practical expedient | Real estate funds |  |
Assets |  |
Other investments | 291,564 | 291,640
Fair value based on NAV practical expedient | Other privately held investments |  |
Assets |  |
Other investments | $ 36,386 | $ 29,751

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