OTHER COMPREHENSIVE INCOME (LOSS) AND ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 277.1	$ 536.4	$ 1,031.4
Other comprehensive income (loss)	3.3	(6.2)	(5.2)
Ending balance	165.7	277.1	536.4
Change in net unrealized gains on investment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5.8)	0.4	5.6
Other comprehensive income (loss) before reclassifications	3.3	(6.9)	(2.8)
Net realized losses (gains) on investments reclassified from AOCI to net loss	0.0	0.7	(2.4)
Other comprehensive income (loss)	3.3	(6.2)	(5.2)
Ending balance	$ (2.5)	$ (5.8)	$ 0.4