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, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	$ 14,836	$ 20,229	$ 32,899	$ 38,166
Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	11,852	15,216	26,911	29,194
Insurance \| Property
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	7,902	6,980	17,842	16,976
Insurance \| Casualty
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	0	0	0	0
Insurance \| Specialty other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	3,950	8,236	9,069	12,218
Reinsurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	2,984	5,013	5,988	8,972
Reinsurance \| Casualty
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	0	0	0	0
Reinsurance \| Specialty other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	2,984	5,013	5,988	8,847
Reinsurance \| Run-off
Liability for Future Policy Benefit, by Product Segment [Line Items]
Prior years - net favorable (adverse) effect	$ 0	$ 0	$ 0	$ 125