Leases - Components of Leases (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 51.2	$ 57.7
Operating lease liabilities	$ 51.4	$ 66.4
Operating lease weighted-average remaining lease term	7 years 8 months 12 days	8 years 2 months 19 days
Operating lease weighted-average discount rate	6.13%	3.44%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Argo Underwriting Agency Limited
Lessee, Lease, Description [Line Items]
Operating lease right-of-use asset reclassified		$ 0.5
Operating lease liabilities reclassified		$ 0.5