Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets:
Net operating loss carryforwards	$ 331.4	$ 299.5
Deferred ceding commission	13.3	8.5
Net unearned premium	8.6	6.6
Stock-based compensation	5.5	5.3
Lease liabilities	4.3	4.7
Depreciation and amortization	3.3	1.4
Charitable contribution	2.3	2.0
Unrealized loss on investments	0.0	0.9
Startup costs	0.4	0.5
Total gross deferred tax assets	369.1	329.4
Deferred tax liabilities:
Right-of-use assets	2.5	2.4
Deferred acquisition costs	(2.5)	(1.8)
Unrealized gain on investments	(0.1)	0.0
Other	0.0	(2.8)
Total gross deferred tax liabilities	(5.1)	(7.0)
Valuation allowance	(364.0)	(322.4)
Total deferred tax assets, net	$ 0.0	$ 0.0