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INVESTMENTS - Carrying Amounts of Investments (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 407.0	$ 349.8
Gross Unrealized Gains	6.9	1.6
Gross Unrealized Losses	(0.5)	(2.7)
Fair Value	413.4	348.6
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0.9	14.4
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	0.9	14.4
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2.6	2.6
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	2.6	2.6
Municipal
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4.9	10.6
Gross Unrealized Gains	0.2	0.1
Gross Unrealized Losses	0.0	(0.1)
Fair Value	5.0	10.6
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	169.9	152.0
Gross Unrealized Gains	3.8	0.8
Gross Unrealized Losses	0.0	(0.9)
Fair Value	173.6	151.9
Mortgage and other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	228.8	170.1
Gross Unrealized Gains	3.0	0.6
Gross Unrealized Losses	(0.5)	(1.7)
Fair Value	$ 231.3	$ 169.1

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