Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Fixed maturities, available-for-sale, amortized cost	$ 148.5	$ 127.3
Short-term investments, amortized cost	188.6	325.6
Accounts receivable, allowance	$ 0.4	$ 0.3
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	80,000,000	80,000,000
Common stock, shares issued (in shares)	23,891,930	23,201,434
Common stock, shares outstanding (in shares)	23,891,930	23,201,434