The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

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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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Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process.

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Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.

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Loss and Loss Adjustment Expense Reserves - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Jun. 30, 2026	Dec. 31, 2025	Jun. 30, 2025	Dec. 31, 2024
Liability for Claims and Claims Adjustment Expense [Line Items]
Loss and loss adjustment expenses	$ 230,400,000	$ 258,500,000		$ 686,800,000
P&C Insurance and Reinsurance (Ark/WM Outrigger)
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable prior loss reserve development	(19,700,000)	(100,000)	$ (66,500,000)	(70,000,000.0)
Loss and loss adjustment expense reserves	2,747,400,000	2,477,900,000	2,747,400,000	2,477,900,000	$ 2,623,800,000	$ 2,481,000,000	$ 2,288,500,000	$ 2,127,500,000
Loss and loss adjustment expenses	230,100,000	254,600,000	612,400,000	652,100,000
P&C Insurance and Reinsurance (Ark/WM Outrigger) \| Operating Segments
Liability for Claims and Claims Adjustment Expense [Line Items]
Loss and loss adjustment expense reserves	2,747,400,000		2,747,400,000			2,481,000,000
Loss and loss adjustment expenses	230,100,000	254,600,000	612,400,000	652,100,000
HG Global \| Operating Segments
Liability for Claims and Claims Adjustment Expense [Line Items]
Loss and loss adjustment expense reserves	0		0			$ 0
Loss and loss adjustment expenses	$ 0	$ 0	$ 0	$ 0