Reinsurance - Unsecured Reinsurance Recoverable by Reinsurer (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 170.4	$ 138.4
Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	173.3	180.4
Lloyd's Underwriter Syndicate no. 2791 MAP | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	2.7	1.7
Lloyd's Underwriter Syndicate no. 1084 CSL | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	1.1	1.6
Top Reinsurers | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	172.9	179.1
Other reinsurers | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	0.4	1.3
A+ | Hannover Rueck SE | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	104.0	126.6
A+ | Swiss Reinsurance America Corporation | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	26.3	20.1
A+ | Aviva Insurance Limited | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	2.1	0.9
A+ | Odyssey Reinsurance Company | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	0.2	0.1
A+ | Lloyd's Underwriter Syndicate No. 2001 AML | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	0.2	0.4
A | MAPFRE Re, Compania De Reaseguros S.A. | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	34.0	27.2
A++ | Tokio Marine & Nichido Fire Insurance Company Limited | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	1.9	0.1
A++ | The Travellers Indemnity Company | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 0.4	$ 0.4