Investments - Fixed Maturities Securities and Short-term Investments (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Amortized Cost
Amortized Cost	$ 450.7	$ 291.7
Amortized Cost	62.8	152.5
Amortized Cost	513.5	444.2
Gross Unrealized Gains
Gross Unrealized Gains	0.1	3.2
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Gains	0.1	3.2
Gross Unrealized Losses
Gross Unrealized Losses	(14.5)	(1.5)
Gross Unrealized Losses	0.0	0.0
Gross Unrealized Losses	(14.5)	(1.5)
Fair Value
Fair Value	436.3	293.4
Fair Value	62.8	152.5
Total investments	499.1	445.9
U.S. government and agencies
Amortized Cost
Amortized Cost	98.7	75.7
Amortized Cost	51.5	103.5
Gross Unrealized Gains
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses
Gross Unrealized Losses	(2.5)	(0.1)
Gross Unrealized Losses	0.0	0.0
Fair Value
Fair Value	96.2	75.7
Fair Value	51.5	103.5
States and other territories
Amortized Cost
Amortized Cost	7.1	8.2
Gross Unrealized Gains
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Losses
Gross Unrealized Losses	(0.3)	(0.1)
Fair Value
Fair Value	6.8	8.2
Corporate securities
Amortized Cost
Amortized Cost	250.0	144.0
Amortized Cost	11.3	49.0
Gross Unrealized Gains
Gross Unrealized Gains	0.1	2.6
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses
Gross Unrealized Losses	(7.9)	(0.2)
Gross Unrealized Losses	0.0	0.0
Fair Value
Fair Value	242.2	146.4
Fair Value	11.3	49.0
Residential mortgage-backed securities
Amortized Cost
Amortized Cost	60.6	38.2
Gross Unrealized Gains
Gross Unrealized Gains	0.0	0.4
Gross Unrealized Losses
Gross Unrealized Losses	(3.6)	(0.9)
Fair Value
Fair Value	57.0	37.7
Commercial mortgage-backed securities
Amortized Cost
Amortized Cost	3.1	5.2
Gross Unrealized Gains
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses
Gross Unrealized Losses	(0.2)	(0.2)
Fair Value
Fair Value	2.9	5.0
Asset backed securities
Amortized Cost
Amortized Cost	31.2	20.4
Gross Unrealized Gains
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses
Gross Unrealized Losses	0.0	0.0
Fair Value
Fair Value	$ 31.2	$ 20.4

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