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Debt - Debt Outstanding (Details) € in Millions, $ in Millions	Dec. 31, 2023 USD ($)	Dec. 31, 2023 EUR (€)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Debt Instrument
Long-term debt, gross	$ 578.9
Carrying Value	564.6		$ 575.2
HG Global Senior Notes
Debt Instrument
Carrying Value	146.9		146.5
Ark 2007 Subordinated Notes
Debt Instrument
Carrying Value	30.0		30.0
Ark 2021 Subordinated Notes
Debt Instrument
Carrying Value	155.5		153.7
Kudu Credit Facility
Debt Instrument
Carrying Value	203.8		208.3
Other Operations debt
Debt Instrument
Carrying Value	28.4		36.7
Senior Notes \| HG Global Senior Notes
Debt Instrument
Long-term debt, gross	150.0		150.0
Unamortized discount and issuance cost	(3.1)		(3.5)
Carrying Value	$ 146.9		$ 146.5
Effective yield (as a percent)	11.90%	11.90%	8.90%
Subordinated Debt \| Ark
Debt Instrument
Carrying Value	$ 185.5		$ 183.7
Effective yield (as a percent)	11.00%	11.00%	7.60%
Subordinated Debt \| Ark 2007 Subordinated Notes
Debt Instrument
Long-term debt, gross	$ 30.0		$ 30.0
Subordinated Debt \| Ark 2021 Subordinated Notes
Debt Instrument
Unamortized issuance cost	(4.2)		(4.6)
Carrying Value	155.5		153.7
Subordinated Debt \| Ark 2021 Subordinated Notes, Tranche 1
Debt Instrument
Long-term debt, gross	42.7	€ 39.1	41.3
Subordinated Debt \| Ark 2021 Subordinated Notes, Tranche 2
Debt Instrument
Long-term debt, gross	47.0		47.0
Subordinated Debt \| Ark 2021 Subordinated Notes, Tranche 3
Debt Instrument
Long-term debt, gross	70.0		70.0
Secured Debt \| Kudu Credit Facility
Debt Instrument
Long-term debt, gross	210.3		215.2
Unamortized issuance cost	(6.5)		(6.9)
Carrying Value	$ 210.3		$ 215.2	$ 225.4	$ 0.0
Effective yield (as a percent)	10.10%	10.10%	6.10%
Secured Debt \| Other Operations debt
Debt Instrument
Long-term debt, gross	$ 28.9		$ 37.4
Unamortized issuance cost	$ (0.5)		$ (0.7)
Effective yield (as a percent)	10.20%	10.20%	6.60%