RESERVE FOR LOSSES AND LOSS EXPENSES - Summary of Reconciliation of Development Tables to Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Claims Development [Line Items]
Net outstanding liabilities	$ 9,722,280
Reinsurance recoverable on unpaid claims	5,831,172	$ 5,017,611	$ 4,496,641	$ 3,877,756
Gross outstanding liabilities	15,553,452
Unallocated claims adjustment expenses	168,308
Foreign exchange and other	21,972
Ceded reserves related to retroactive transactions	(574,869)
Reserve for losses and loss expenses	15,168,863	$ 14,653,094	$ 13,926,766	$ 12,752,081
Insurance
Claims Development [Line Items]
Net outstanding liabilities	4,503,262
Reinsurance recoverable on unpaid claims	4,133,206
Gross outstanding liabilities	8,636,468
Insurance | Property
Claims Development [Line Items]
Net outstanding liabilities	624,924
Reinsurance recoverable on unpaid claims	398,826
Gross outstanding liabilities	1,023,750
Insurance | Accident and health
Claims Development [Line Items]
Net outstanding liabilities	76,862
Reinsurance recoverable on unpaid claims	6,518
Gross outstanding liabilities	83,380
Insurance | Marine and aviation
Claims Development [Line Items]
Net outstanding liabilities	605,168
Reinsurance recoverable on unpaid claims	278,976
Gross outstanding liabilities	884,144
Insurance | Cyber
Claims Development [Line Items]
Net outstanding liabilities	296,401
Reinsurance recoverable on unpaid claims	393,436
Gross outstanding liabilities	689,837
Insurance | Professional lines
Claims Development [Line Items]
Net outstanding liabilities	1,793,131
Reinsurance recoverable on unpaid claims	1,474,539
Gross outstanding liabilities	3,267,670
Insurance | Credit and political risk
Claims Development [Line Items]
Net outstanding liabilities	102,547
Reinsurance recoverable on unpaid claims	34,391
Gross outstanding liabilities	136,938
Insurance | Liability
Claims Development [Line Items]
Net outstanding liabilities	1,004,229
Reinsurance recoverable on unpaid claims	1,546,520
Gross outstanding liabilities	2,550,749
Reinsurance
Claims Development [Line Items]
Net outstanding liabilities	5,219,018
Reinsurance recoverable on unpaid claims	1,697,966
Gross outstanding liabilities	6,916,984
Reinsurance | Accident and health
Claims Development [Line Items]
Net outstanding liabilities	236,094
Reinsurance recoverable on unpaid claims	38,647
Gross outstanding liabilities	274,741
Reinsurance | Marine and aviation
Claims Development [Line Items]
Net outstanding liabilities	156,073
Reinsurance recoverable on unpaid claims	57,692
Gross outstanding liabilities	213,765
Reinsurance | Professional lines
Claims Development [Line Items]
Net outstanding liabilities	998,587
Reinsurance recoverable on unpaid claims	303,849
Gross outstanding liabilities	1,302,436
Reinsurance | Liability
Claims Development [Line Items]
Net outstanding liabilities	1,504,428
Reinsurance recoverable on unpaid claims	527,513
Gross outstanding liabilities	2,031,941
Reinsurance | Agriculture
Claims Development [Line Items]
Net outstanding liabilities	131,369
Reinsurance recoverable on unpaid claims	10,018
Gross outstanding liabilities	141,387
Reinsurance | Credit and surety
Claims Development [Line Items]
Net outstanding liabilities	231,515
Reinsurance recoverable on unpaid claims	79,309
Gross outstanding liabilities	310,824
Reinsurance | Motor
Claims Development [Line Items]
Net outstanding liabilities	1,002,332
Reinsurance recoverable on unpaid claims	258,483
Gross outstanding liabilities	1,260,815
Reinsurance | Run Off Lines
Claims Development [Line Items]
Net outstanding liabilities	958,620
Reinsurance recoverable on unpaid claims	422,455
Gross outstanding liabilities	$ 1,381,075