FAIR VALUE MEASUREMENTS - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	$ 16,083,046	$ 14,351,402
Short term investments	6,519,207	4,669,272
Equity investments trading	95,342	625,058
Other investments	3,167,941	2,494,954
Derivative assets	18,233	44,421
Derivative liabilities	(35,557)	(7,581)
Total other assets	3,141	3,499
Total other liabilities	(3,686)	(5,331)
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	16,083,046	14,351,402
Short term investments	6,519,207	4,669,272
Equity investments trading	95,342	625,058
Other investments	3,167,941	2,494,954
Assumed and ceded (re)insurance contracts	(545)	(1,832)
Derivative assets	18,233	44,400
Derivative liabilities	(35,557)	(7,560)
Total other assets		35,008
Total other liabilities	(17,869)
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs	25,847,667	22,175,694
Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	1,864,201	1,408,248
Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	8,587,946	7,180,129
Short term investments	67,176	0
Equity investments trading	95,342	625,058
Other investments	0	0
Assumed and ceded (re)insurance contracts	0	0
Derivative assets	6,819	387
Derivative liabilities	(7,139)	(2,008)
Total other liabilities	(320)	(1,621)
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs	8,750,144	7,803,566
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	7,495,100	7,171,273
Short term investments	6,452,031	4,669,272
Equity investments trading	0	0
Other investments	1,697,810	1,241,468
Assumed and ceded (re)insurance contracts	0	0
Derivative assets	11,414	44,013
Derivative liabilities	(28,418)	(5,552)
Total other assets		38,461
Total other liabilities	(17,004)
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs	15,627,937	13,120,474
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Short term investments	0	0
Equity investments trading	0	0
Other investments	166,391	166,780
Assumed and ceded (re)insurance contracts	(545)	(1,832)
Derivative assets	0	0
Derivative liabilities	0	0
Total other liabilities	(545)	(1,832)
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs	165,846	164,948
Significant Unobservable Inputs (Level 3) | Other assets | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assumed and ceded (re)insurance contracts	(3,200)	(3,500)
Significant Unobservable Inputs (Level 3) | Other liabilities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assumed and ceded (re)insurance contracts	(3,700)	(5,300)
U.S. treasuries | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	8,587,946	7,180,129
U.S. treasuries | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	8,587,946	7,180,129
U.S. treasuries | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
U.S. treasuries | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Corporate | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	4,482,082	4,390,568
Corporate | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Corporate | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	4,482,082	4,390,568
Corporate | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Agencies | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	460,936	395,149
Agencies | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Agencies | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	460,936	395,149
Agencies | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Non-U.S. government | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	403,758	383,838
Non-U.S. government | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Non-U.S. government | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	403,758	383,838
Non-U.S. government | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Residential mortgage-backed | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	806,120	710,429
Residential mortgage-backed | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Residential mortgage-backed | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	806,120	710,429
Residential mortgage-backed | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Commercial mortgage-backed | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	210,942	213,987
Commercial mortgage-backed | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Commercial mortgage-backed | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	210,942	213,987
Commercial mortgage-backed | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Asset-backed | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	1,131,262	1,077,302
Asset-backed | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Asset-backed | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	1,131,262	1,077,302
Asset-backed | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity investments trading	0	0
Catastrophe bonds | Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	1,697,810	1,241,468
Catastrophe bonds | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Catastrophe bonds | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	1,697,810	1,241,468
Catastrophe bonds | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Term loans | Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	98,876	100,000
Term loans | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Term loans | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Term loans | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	98,876	100,000
Direct private equity investments | Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	67,515	66,780
Direct private equity investments | Quoted Prices in Active Markets for Identical  Assets (Level 1) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Direct private equity investments | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Direct private equity investments | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	67,515	66,780
Fund investments | Fair Value Measured at Net Asset Value Per Share | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	$ 1,303,740	$ 1,086,706