Leases - Schedule of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 42.9	$ 37.6
Lease liability	$ 45.9	$ 38.3
Operating lease, weighted average incremental borrowing rate, percent	5.00%	4.60%
HG/BAM
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 8.0	$ 10.1
Lease liability	8.6	10.1
Ark
Lessee, Lease, Description [Line Items]
ROU lease asset	7.0
Lease liability	7.0
NSM
Lessee, Lease, Description [Line Items]
ROU lease asset	13.8	17.1
Lease liability	15.0	17.1
Kudu
Lessee, Lease, Description [Line Items]
ROU lease asset	6.7	2.0
Lease liability	7.1	2.0
Other Operations
Lessee, Lease, Description [Line Items]
ROU lease asset	7.4	8.4
Lease liability	$ 8.2	$ 9.1