FINANCIAL INSTRUMENTS AND FAIR VALUE - Schedule of Investments at Fair Value (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	$ 332.9	$ 240.4
Total
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4.8	6.6
Total Investments, at fair value	332.9	240.4
Total | Total debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	332.9	191.7
Total | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	6.2	5.4
Total | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	13.5	11.6
Total | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	30.1	22.4
Total | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	132.2	79.7
Total | Mortgage and other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	150.9	72.6
Total | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value		48.7
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4.8	6.6
Total Investments, at fair value	15.5	60.9
Level 1 | Total debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	15.5	12.2
Level 1 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	2.0	0.6
Level 1 | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	13.5	11.6
Level 1 | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 1 | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 1 | Mortgage and other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 1 | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value		48.7
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0.0	0.0
Total Investments, at fair value	317.4	179.5
Level 2 | Total debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	317.4	179.5
Level 2 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	4.2	4.8
Level 2 | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 2 | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	30.1	22.4
Level 2 | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	132.2	79.7
Level 2 | Mortgage and other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	150.9	72.6
Level 2 | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value		0.0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0.0	0.0
Total Investments, at fair value	0.0	0.0
Level 3 | Total debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 3 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 3 | U.S Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 3 | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 3 | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	0.0	0.0
Level 3 | Mortgage and other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value	$ 0.0	0.0
Level 3 | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Investments, at fair value		$ 0.0