FAIR VALUE MEASUREMENTS - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Assets
Fixed maturities, available for sale	$ 11,326,894	$ 12,313,200
Equity securities	485,253	655,675
Other investments	996,751	947,982
Short-term investments	70,310	31,063
Derivative instruments	37,682	3,116
Total Assets	12,916,890	13,951,036
Liabilities
Derivative instruments	703	20,617
Cash-settled awards	4,792	9,091
Total Liabilities	5,495	29,708
U.S. government and agency
Assets
Fixed maturities, available for sale	2,639,330	2,682,448
Non-U.S. government
Assets
Fixed maturities, available for sale	562,029	795,178
Corporate debt
Assets
Fixed maturities, available for sale	4,255,556	4,495,312
Agency RMBS
Assets
Fixed maturities, available for sale	1,202,785	1,074,589
CMBS
Assets
Fixed maturities, available for sale	947,778	1,248,191
Non-agency RMBS
Assets
Fixed maturities, available for sale	133,534	186,164
ABS
Assets
Fixed maturities, available for sale	1,429,527	1,622,480
Municipals
Assets
Fixed maturities, available for sale	156,355	208,838
Common stocks
Assets
Equity securities	7,473	1,364
Preferred stocks
Assets
Equity securities	72	179
Exchange-traded funds
Assets
Equity securities	269,806	336,815
Bond mutual funds
Assets
Equity securities	207,902	317,317
Hedge funds
Assets
Other investments	32,616	59,488
Direct lending funds
Assets
Other investments	258,626	289,867
Private equity funds
Assets
Other investments	265,836	249,974
Real estate funds
Assets
Other investments	298,499	238,222
CLO-Equities
Assets
Other investments	5,016	5,910
Other privately held investments
Assets
Other investments	136,158	104,521
Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed maturities, available for sale	2,600,636	2,632,541
Equity securities	277,351	338,358
Other investments	0	0
Short-term investments	0	0
Derivative instruments	0	0
Total Assets	2,877,987	2,970,899
Liabilities
Derivative instruments	0	0
Cash-settled awards	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	2,600,636	2,632,541
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	7,473	1,364
Quoted prices in active markets for identical assets (Level 1) | Preferred stocks
Assets
Equity securities	72	179
Quoted prices in active markets for identical assets (Level 1) | Exchange-traded funds
Assets
Equity securities	269,806	336,815
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) | Hedge 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) | CLO-Equities
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	8,607,154	9,637,765
Equity securities	207,902	317,317
Other investments	0	0
Short-term investments	70,310	31,063
Derivative instruments	37,682	3,116
Total Assets	8,923,048	9,989,261
Liabilities
Derivative instruments	703	14,987
Cash-settled awards	4,792	9,091
Total Liabilities	5,495	24,078
Significant other observable inputs (Level 2) | U.S. government and agency
Assets
Fixed maturities, available for sale	38,694	49,907
Significant other observable inputs (Level 2) | Non-U.S. government
Assets
Fixed maturities, available for sale	562,029	795,178
Significant other observable inputs (Level 2) | Corporate debt
Assets
Fixed maturities, available for sale	4,136,452	4,452,418
Significant other observable inputs (Level 2) | Agency RMBS
Assets
Fixed maturities, available for sale	1,202,785	1,074,589
Significant other observable inputs (Level 2) | CMBS
Assets
Fixed maturities, available for sale	947,778	1,248,191
Significant other observable inputs (Level 2) | Non-agency RMBS
Assets
Fixed maturities, available for sale	133,534	186,164
Significant other observable inputs (Level 2) | ABS
Assets
Fixed maturities, available for sale	1,429,527	1,622,480
Significant other observable inputs (Level 2) | Municipals
Assets
Fixed maturities, available for sale	156,355	208,838
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	0
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	207,902	317,317
Significant other observable inputs (Level 2) | Hedge 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) | CLO-Equities
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	119,104	42,894
Equity securities	0	0
Other investments	141,174	110,431
Short-term investments	0	0
Derivative instruments	0	0
Total Assets	260,278	153,325
Liabilities
Derivative instruments	0	5,630
Cash-settled awards	0	0
Total Liabilities	0	5,630
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	119,104	42,894
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	0	0
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) | Hedge 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) | CLO-Equities
Assets
Other investments	5,016	5,910
Significant unobservable inputs (Level 3) | Other privately held investments
Assets
Other investments	136,158	104,521
Fair value based on NAV practical expedient
Assets
Other investments	855,577	837,551
Total Assets	855,577	837,551
Fair value based on NAV practical expedient | Hedge funds
Assets
Other investments	32,616	59,488
Fair value based on NAV practical expedient | Direct lending funds
Assets
Other investments	258,626	289,867
Fair value based on NAV practical expedient | Private equity funds
Assets
Other investments	265,836	249,974
Fair value based on NAV practical expedient | Real estate funds
Assets
Other investments	298,499	238,222
Fair value based on NAV practical expedient | CLO-Equities
Assets
Other investments	0	0
Fair value based on NAV practical expedient | Other privately held investments
Assets
Other investments	$ 0	$ 0