Reinsurance - Unsecured Reinsurance Recoverable by Reinsurer (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 138.4	$ 156.8
Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	180.4	159.6
Lloyd's Underwriter Syndicate no. 2791 MAP | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	1.7	1.0
Lloyd's Underwriter Syndicate No. 1084 CSL | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	1.6	4.3
Lloyd's Underwriter Syndicate no. 2001 AML | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	0.4	0.5
Lloyd's Underwriter Syndicate No. 2987 BRT | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	0.2	0.0
Top Reinsurers | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	179.3	157.7
Other reinsurers | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	1.1	1.9
A+ | Hannover Rueck SE | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	126.6	100.1
A+ | Swiss Reinsurance America Corporation | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	20.1	27.6
A+ | Aviva Insurance Limited | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	0.9	0.0
A+ | Munich Reinsurance America Inc | 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	27.2	23.8
A++ | The Travellers Indemnity Company | Ceded Credit Risk, Unsecured
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 0.4	$ 0.0