Leases - Components of Leases (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 57.7	$ 81.4
Operating lease liabilities	$ 66.4	$ 97.7
Operating lease weighted-average remaining lease term	8 years 2 months 19 days	9 years 6 months 3 days
Operating lease weighted-average discount rate	3.44%	3.53%
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