Municipal Bond Guarantee Insurance - Schedule of Municipal Bond Guarantee Insured Obligations (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($) contract	Dec. 31, 2024 USD ($) contract
Subsidiary - HG Global | Maximum
Guarantor Obligations [Line Items]
Percentage of par value of policy reinsured	15.00%
HG Global
Guarantor Obligations [Line Items]
Contracts outstanding | contract	16,914	15,884
Remaining weighted average contract period (in years)	11 years 6 months	11 years 2 months 12 days
Outstanding first loss exposure from policies assumed (in millions)	$ 19,910.4	$ 18,503.3
Gross unearned insurance premiums (in millions)	$ 316.3	$ 297.3