CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Fixed maturities available-for-sale, amortized cost	$ 607.0	$ 632.0
Short-term investments, cost	31.1	45.8
Premium receivable, allowance for doubtful accounts	$ 2.8	$ 2.5
Common stock, par value (usd per share)	$ 0.00001	$ 0.00001
Common stock, authorized (in shares)	200,000,000	200,000,000
Common stock, issued (in shares)	71,378,678	70,163,703
Common stock, outstanding (in shares)	71,378,678	70,163,703