INVESTMENTS - Credit Ratings (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 272.7	$ 169.3
Fair Value	274.8	166.8
AAA
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	69.3	53.0
Fair Value	$ 69.7	$ 52.1
AAA | AFS securities | Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage (in percent)	25.40%	31.20%
AA+, AA, AA-, A-1
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 114.5	$ 59.4
Fair Value	$ 115.7	$ 58.8
AA+, AA, AA-, A-1 | AFS securities | Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage (in percent)	42.10%	35.30%
A+, A, A-
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 69.5	$ 42.1
Fair Value	$ 69.9	$ 41.2
A+, A, A- | AFS securities | Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage (in percent)	25.40%	24.70%
BBB+, BBB, BBB-
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 19.4	$ 14.8
Fair Value	$ 19.5	$ 14.7
BBB+, BBB, BBB- | AFS securities | Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage (in percent)	7.10%	8.80%
Standard & Poor's Global Rating, Total | AFS securities | Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage (in percent)	100.00%	100.00%