v3.26.1
FAIR VALUE MEASUREMENTS - Financial Instruments Measured at Fair Value (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Assets    
Fixed maturities, available for sale $ 13,828,314 $ 13,018,027
Equity securities 748,532 707,569
Other investments 1,062,933 1,027,798
Short-term investments 2,828 20,298
Derivative instruments (refer to Note 5) 8,621 930
Total Assets 15,651,228 14,774,622
Liabilities    
Derivative instruments (refer to Note 5) 1,627 8,859
Total Liabilities 1,627 8,859
U.S. government and agency    
Assets    
Fixed maturities, available for sale 2,387,374 2,417,901
Non-U.S. government    
Assets    
Fixed maturities, available for sale 823,910 810,544
Corporate debt    
Assets    
Fixed maturities, available for sale 5,584,899 5,222,433
Agency RMBS    
Assets    
Fixed maturities, available for sale 2,422,949 2,035,352
CMBS    
Assets    
Fixed maturities, available for sale 788,348 801,511
Non-agency RMBS    
Assets    
Fixed maturities, available for sale 208,039 190,124
ABS    
Assets    
Fixed maturities, available for sale 1,567,259 1,488,067
Municipals    
Assets    
Fixed maturities, available for sale 45,536 52,095
Common stocks    
Assets    
Equity securities 3,285 13,695
Preferred stocks    
Assets    
Equity securities 48,841 20,311
Exchange-traded funds    
Assets    
Equity securities 435,135 401,757
Bond mutual funds    
Assets    
Equity securities 261,271 271,806
Multi-strategy funds    
Assets    
Other investments 6,963 11,577
Direct lending funds    
Assets    
Other investments 194,209 186,747
Private equity funds    
Assets    
Other investments 400,067 364,376
Real estate funds    
Assets    
Other investments 278,438 291,491
Other privately held investments    
Assets    
Other investments 183,256 173,607
Quoted prices in active markets for identical assets (Level 1)    
Assets    
Fixed maturities, available for sale 2,345,018 2,385,085
Equity securities 487,261 429,691
Other investments 0 0
Short-term investments 0 0
Derivative instruments (refer to Note 5) 0 0
Total Assets 2,832,279 2,814,776
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 2,345,018 2,385,085
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 3,285 13,695
Quoted prices in active markets for identical assets (Level 1) | Preferred stocks    
Assets    
Equity securities 48,841 14,239
Quoted prices in active markets for identical assets (Level 1) | Exchange-traded funds    
Assets    
Equity securities 435,135 401,757
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 11,189,749 10,404,314
Equity securities 261,271 277,878
Other investments 0 0
Short-term investments 2,828 20,298
Derivative instruments (refer to Note 5) 8,621 930
Total Assets 11,462,469 10,703,420
Liabilities    
Derivative instruments (refer to Note 5) 1,627 8,859
Total Liabilities 1,627 8,859
Significant other observable inputs (Level 2) | U.S. government and agency    
Assets    
Fixed maturities, available for sale 42,356 32,816
Significant other observable inputs (Level 2) | Non-U.S. government    
Assets    
Fixed maturities, available for sale 823,910 810,544
Significant other observable inputs (Level 2) | Corporate debt    
Assets    
Fixed maturities, available for sale 5,361,369 5,033,161
Significant other observable inputs (Level 2) | Agency RMBS    
Assets    
Fixed maturities, available for sale 2,422,949 2,035,352
Significant other observable inputs (Level 2) | CMBS    
Assets    
Fixed maturities, available for sale 788,348 801,511
Significant other observable inputs (Level 2) | Non-agency RMBS    
Assets    
Fixed maturities, available for sale 208,039 190,124
Significant other observable inputs (Level 2) | ABS    
Assets    
Fixed maturities, available for sale 1,497,242 1,448,711
Significant other observable inputs (Level 2) | Municipals    
Assets    
Fixed maturities, available for sale 45,536 52,095
Significant other observable inputs (Level 2) | Common stocks    
Assets    
Equity securities 0 0
Significant other observable inputs (Level 2) | Preferred stocks    
Assets    
Equity securities 0 6,072
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 261,271 271,806
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 293,547 228,628
Equity securities 0 0
Other investments 131,224 123,925
Short-term investments 0 0
Derivative instruments (refer to Note 5) 0 0
Total Assets 424,771 352,553
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 223,530 189,272
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 70,017 39,356
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 131,224 123,925
Fair value based on NAV practical expedient    
Assets    
Other investments 931,709 903,873
Total Assets 931,709 903,873
Fair value based on NAV practical expedient | Multi-strategy funds    
Assets    
Other investments 6,963 11,577
Fair value based on NAV practical expedient | Direct lending funds    
Assets    
Other investments 194,209 186,747
Fair value based on NAV practical expedient | Private equity funds    
Assets    
Other investments 400,067 364,376
Fair value based on NAV practical expedient | Real estate funds    
Assets    
Other investments 278,438 291,491
Fair value based on NAV practical expedient | Other privately held investments    
Assets    
Other investments $ 52,032 $ 49,682