Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 08, 2021 USD ($)
Accounting Policies [Abstract]
Number of reportable segments | segment	1
Premium receivable, allowance for doubtful accounts	$ 1.6	$ 0.5
Amortization of net deferred acquisition costs	9.5	4.9	$ 2.1
Matching contributions	0.9	0.5	0.3
Advertising expenses	104.6	58.3	$ 76.0
Other Assets
Accounting Policies [Abstract]
Operating lease, right-of-use asset	(21.9)	0.0
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset	$ 21.9	$ 0.0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period	4 years
ASU 2016-02 | Other Assets
Accounting Policies [Abstract]
Operating lease, right-of-use asset	$ (16.9)			$ (0.3)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset	16.9			0.3
ASU 2016-02 | Other Liabilities
Accounting Policies [Abstract]
Operating lease liability	17.2
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability	$ 17.2
Deferred rent credit				$ (0.3)