RESERVE FOR LOSSES AND LOSS EXPENSES - Prior Year Reserve Development By Segment and Line of Business (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	$ 17,937	$ 0
Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	13,978	0
Insurance | Property
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	9,996	8,011
Insurance | Casualty
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	0	0
Insurance | Specialty other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	3,982	(8,011)
Reinsurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	3,959	0
Reinsurance | Casualty
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	0	0
Reinsurance | Specialty other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	3,834	0
Reinsurance | Run-off
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	$ 125	$ 0