LOSS AND LOSS ADJUSTMENT EXPENSE RESERVES (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross loss and LAE reserves, January 1			$ 237.2	$ 140.7
Reinsurance recoverable on unpaid losses			(79.6)	(18.9)
Net loss and LAE reserves, January 1			157.6	121.8
Net incurred loss and LAE related to:
Current year			293.8	282.0
Prior years			(9.3)	21.3
Total incurred	$ 114.4	$ 76.1	284.5	303.3
Net paid loss and LAE related to:
Current year			150.4	165.8
Prior years			72.6	100.4
Total paid			223.0	266.2
Net loss and LAE reserves, September 30	219.1	158.9	219.1	158.9
Plus reinsurance recoverable on unpaid losses	81.6	66.4	81.6	66.4
Gross loss and LAE reserves, September 30	$ 300.7	$ 225.3	$ 300.7	$ 225.3