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