INVESTMENTS - Amortized Cost and Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Total	$ 218.9	$ 122.2
Gross Unrealized Gains	5.8	0.8
Gross Unrealized Losses	(0.2)	(0.2)
Fair Value	224.5	122.8
U.S. Treasury securities and agencies
Debt Securities, Available-for-sale [Line Items]
Total	5.1	12.7
Gross Unrealized Gains	0.1	0.1
Gross Unrealized Losses	0.0	0.0
Fair Value	5.2	12.8
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Total	20.2	10.2
Gross Unrealized Gains	0.8	0.1
Gross Unrealized Losses	0.0	0.0
Fair Value	21.0	10.3
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Total	95.8	38.8
Gross Unrealized Gains	3.1	0.4
Gross Unrealized Losses	0.0	(0.1)
Fair Value	98.9	39.1
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Total	11.1	3.3
Gross Unrealized Gains	0.1	0.0
Gross Unrealized Losses	(0.1)	0.0
Fair Value	11.1	3.3
Commercial mortgage backed securities
Debt Securities, Available-for-sale [Line Items]
Total	57.9	31.5
Gross Unrealized Gains	1.2	0.1
Gross Unrealized Losses	(0.1)	(0.1)
Fair Value	59.0	31.5
Other debt obligations
Debt Securities, Available-for-sale [Line Items]
Total	28.8	25.7
Gross Unrealized Gains	0.5	0.1
Gross Unrealized Losses	0.0	0.0
Fair Value	$ 29.3	$ 25.8