LOSS AND LOSS ADJUSTMENT EXPENSE RESERVES - Schedule of Reserve Balance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross loss and LAE reserves, January 1			$ 284.2	$ 287.4
Reinsurance recoverable on unpaid losses			(43.8)	(76.4)
Net loss and LAE reserves, January 1	$ 342.1	$ 214.9	342.1	214.9	$ 240.4	$ 211.0
Net incurred loss and LAE related to:
Current year			549.1	209.2
Prior years			(7.9)	(0.6)
Total incurred	184.5	85.8	541.2	208.6
Net paid loss and LAE related to:
Current year			293.2	87.4
Prior years			146.3	117.3
Total paid			439.5	204.7
Net loss and LAE reserves, September 30	342.1	214.9	342.1	214.9
Plus reinsurance recoverable on unpaid losses	50.3	41.6	50.3	41.6
Gross loss and LAE reserves, September 30	$ 392.4	$ 256.5	$ 392.4	$ 256.5