Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating loss carryforwards	$ 262.2	$ 127.4
Deferred ceding commission	8.6	7.8
Lease liabilities	5.6	3.4
Unrealized loss on investments	5.5	0.0
Net unearned premium	5.3	2.6
Stock-based compensation	3.7	2.4
Charitable contribution	1.6	0.9
Startup costs	0.5	0.7
Other	0.0	0.6
Total gross deferred tax assets	293.0	145.8
Deferred tax liabilities:
Right-of-use assets	(3.8)	(3.3)
Depreciation and amortization	(1.0)	(2.2)
Deferred acquisition costs	(1.4)	(1.3)
Other	(3.8)	0.0
Total gross deferred tax liabilities	(10.0)	(6.8)
Valuation allowance	(283.0)	(139.0)
Total deferred tax assets, net	$ 0.0	$ 0.0