Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2023
Investments, Owned, Federal Income Tax Note [Line Items]
Net deferred tax benefit	$ 73.0		$ 68.0
Effective tax rate	13.30%	4.60%
P&C Insurance and Reinsurance (Ark/WM Outrigger) \| Ark
Investments, Owned, Federal Income Tax Note [Line Items]
Net deferred tax benefit	$ 51.0		51.0
Financial Guarantee (HG Global) \| HG Global
Investments, Owned, Federal Income Tax Note [Line Items]
Net deferred tax benefit	22.0		$ 17.0
Deferred tax liabilities	$ 5.0

Amount of other deferred income tax expense (benefit) pertaining to income (loss) from continuing operations. For example, but not limited to, acquisition-date income tax benefits or expenses recognized from changes in the acquirer's valuation allowance for its previously existing deferred tax assets resulting from a business combination and adjustments to beginning-of-year balance of a valuation allowance because of a change in circumstance causing a change in judgment about the realizability of the related deferred tax asset in future periods.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 946
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