CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Fixed maturities available-for-sale, amortized cost	$ 698.4	$ 696.8
Short -term investments, cost	85.9	110.4
Premium receivable, allowance for doubtful accounts	$ 2.2	$ 1.6
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)	61,867,577	61,660,996
Common stock, outstanding (in shares)	61,867,577	61,660,996