Investments - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Net Investment Income [Line Items]
Total	$ 9.8	$ 9.5	$ 19.7	$ 19.1
Investment expense	0.1	0.1	0.2	0.2
Net investment income	9.7	9.4	19.5	18.9
Interest on cash and cash equivalents
Net Investment Income [Line Items]
Total			4.0	4.2
Net investment income	1.9	2.1
Fixed maturities
Net Investment Income [Line Items]
Total			15.5	14.4
Net investment income	7.8	7.2
Short-term investments
Net Investment Income [Line Items]
Total			$ 0.2	$ 0.5
Net investment income	$ 0.1	$ 0.2