Debt - Summary of Debt Outstanding (Details) € in Millions, $ in Millions	Mar. 31, 2024 USD ($)	Mar. 31, 2024 EUR (€)	Dec. 31, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Debt Instrument
Total debt	$ 532.1		$ 534.6
Ark 2021 Subordinated Notes
Debt Instrument
Total debt	155.4		155.5
HG Global Senior Notes
Debt Instrument
Total debt	147.0		146.9
Kudu Credit Facility
Debt Instrument
Total debt	203.8		203.8
Other Operations debt
Debt Instrument
Total debt	25.9		28.4
Subordinated Debt | Ark
Debt Instrument
Total debt	$ 155.4		$ 185.5
Effective Rate	13.10%	13.10%	11.00%
Subordinated Debt | Ark 2007 Notes | Ark Subordinated Debt
Debt Instrument
Total debt	$ 0.0		$ 30.0
Subordinated Debt | Ark 2021 Subordinated Notes
Debt Instrument
Unamortized issuance cost	(4.0)		(4.2)
Total debt	155.4		155.5
Subordinated Debt | Ark 2021 Subordinated Notes Tranche 1
Debt Instrument
Amount borrowed	42.4	€ 39.1	42.7
Subordinated Debt | Ark 2021 Subordinated Notes Tranche 2
Debt Instrument
Amount borrowed	47.0		47.0
Subordinated Debt | Ark 2021 Subordinated Notes Tranche 3
Debt Instrument
Amount borrowed	70.0		70.0
Senior Notes | HG Global Senior Notes
Debt Instrument
Amount borrowed	150.0		150.0
Unamortized discount and issuance cost	(3.0)		(3.1)
Total debt	$ 147.0		$ 146.9
Effective Rate	11.90%	11.90%	11.90%
Secured Debt | Kudu Credit Facility
Debt Instrument
Amount borrowed	$ 210.3		$ 210.3
Unamortized issuance cost	(6.5)		(6.5)
Total debt	$ 210.3		$ 210.3	$ 198.3	$ 215.2
Effective Rate	10.60%	10.60%	10.10%
Secured Debt | Other Operations debt
Debt Instrument
Amount borrowed	$ 26.4		$ 28.9
Unamortized issuance cost	$ (0.5)		$ (0.5)
Effective Rate	10.20%	10.20%	10.20%