RESERVE FOR LOSSES AND LOSS EXPENSES - Prior Year Reserve Development By Segment and Line of Business (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($) claim	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	$ 8,012	$ 2,762	$ 8,011	$ 13,118
Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	4,009	1,609	4,008	5,433
Insurance \| Property
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	2,043	$ (10,068)	10,053	(4,376)
Number of prior year claims \| claim		2
Insurance \| Accident and health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	1,966	$ (5,213)	1,966	(5,765)
Insurance \| Marine and aviation
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	19,472	(8,011)	35,374
Insurance \| Cyber
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	10,869	0	19,997
Insurance \| Professional lines
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	(4,383)	0	(20,475)
Insurance \| Credit and political risk
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	3,374	0	16,323
Insurance \| Liability
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	(12,442)	0	(35,645)
Reinsurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	4,003	1,153	4,003	7,685
Reinsurance \| Accident and health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	5,842	0	20,115
Reinsurance \| Marine and aviation
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	3,576	0	8,523
Reinsurance \| Professional lines
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	(9,044)	0	(22,772)
Reinsurance \| Liability
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	(15,222)	0	(55,092)
Reinsurance \| Agriculture
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	729	0	14,741
Reinsurance \| Credit and surety
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	4,003	9,625	4,003	8,498
Reinsurance \| Motor
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	(1,302)	0	(23,248)
Reinsurance \| Run-Off Lines
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	6,949	0	56,920
Reinsurance \| Run-Off Lines \| Property
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	3,421	0	12,568
Reinsurance \| Run-Off Lines \| Catastrophe
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	0	1,436	0	39,982
Reinsurance \| Run-Off Lines \| Engineering
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable (adverse) prior year reserve development	$ 0	$ 2,092	$ 0	$ 4,370