Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Deferred tax assets:
Net operating loss carryforwards	$ 359.9	$ 331.4
Net unearned premium	18.3	8.6
Deferred ceding commission	6.5	13.3
Stock-based compensation	6.1	5.5
Depreciation and amortization	4.8	3.3
Lease liabilities	2.5	2.3
Lease liabilities	1.6	4.3
Startup costs	0.3	0.4
Total gross deferred tax assets	400.0	369.1
Deferred tax liabilities:
Deferred acquisition costs	(2.5)	(2.5)
Right-of-use assets	(1.1)	(2.5)
Unrealized gain on investments	(0.6)	(0.1)
Total gross deferred tax liabilities	(4.2)	(5.1)
Valuation allowance	(395.8)	(364.0)
Total deferred tax assets, net	$ 0.0	$ 0.0