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, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	$ 20,229	$ 0	$ 38,166	$ 0
Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	15,216	0	29,194	0
Insurance | Property
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	6,980	0	16,976	8,011
Insurance | Casualty
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	0	0	0	0
Insurance | Specialty other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	8,236	0	12,218	(8,011)
Reinsurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	5,013	0	8,972	0
Reinsurance | Casualty
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	0	0	0	0
Reinsurance | Specialty other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	5,013	0	8,847	0
Reinsurance | Run-off
Liability for Future Policy Benefit, by Product Segment [Line Items]
Net favorable prior year reserve development	$ 0	$ 0	$ 125	$ 0