RESERVE FOR LOSSES AND LOSS EXPENSES - Prior Year Reserve Development By Segment and Line of Business (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	$ 6,319	$ 3,940	$ 10,357	$ 12,897
Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	2,784	2,773	3,825	9,838
Insurance | Property
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(208)	2,721	5,692	10,783
Insurance | Accident and health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(248)	(1,334)	(552)	2,298
Insurance | Marine and aviation
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	2,682	2,927	15,903	17,575
Insurance | Cyber
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	676	7,783	9,128	7,097
Insurance | Professional lines
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(3,498)	(2,350)	(16,092)	(8,286)
Insurance | Credit and political risk
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	8,430	4,287	12,949	5,182
Insurance | Liability
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(5,050)	(11,261)	(23,203)	(24,811)
Reinsurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	3,535	1,167	6,532	3,059
Reinsurance | Accident and health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	7,000		14,000
Reinsurance | Marine and aviation
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	5,000		5,000
Reinsurance | Professional lines
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(11,000)	(6,000)	(14,000)	(31,000)
Reinsurance | Liability
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(7,000)	(7,000)	(40,000)	(11,000)
Reinsurance | Agriculture
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect		7,000	14,000	8,000
Reinsurance | Credit and surety
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect		4,000		11,000
Reinsurance | Motor
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(5,000)	4,000	(22,000)
Reinsurance | Run-Off Lines
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	11,860	(1,883)	49,971	21,673
Reinsurance | Run-Off Lines | Property
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	2,264	2,053	9,147	24,592
Reinsurance | Run-Off Lines | Catastrophe
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	7,487	(694)	38,546	(940)
Reinsurance | Run-Off Lines | Engineering
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	2,109	(3,242)	2,278	(1,979)
Reinsurance | Non Run-Off Lines
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(8,325)	3,050	(43,439)	(18,614)
Reinsurance | Non Run-Off Lines | Accident and health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	7,284	2,186	14,273	1,687
Reinsurance | Non Run-Off Lines | Marine and aviation
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	5,197	(896)	4,947	(400)
Reinsurance | Non Run-Off Lines | Professional lines
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(10,504)	(6,000)	(13,728)	(30,522)
Reinsurance | Non Run-Off Lines | Liability
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(7,017)	(6,823)	(39,870)	(10,928)
Reinsurance | Non Run-Off Lines | Agriculture
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	2,122	7,141	14,013	8,372
Reinsurance | Non Run-Off Lines | Credit and surety
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	(582)	3,582	(1,128)	11,047
Reinsurance | Non Run-Off Lines | Motor
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	$ (4,825)	$ 3,860	$ (21,946)	$ 2,130