Municipal Bond Guarantee Insurance - Narrative (Details) - USD ($)	1 Months Ended		3 Months Ended	6 Months Ended		12 Months Ended
	May 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2018	Jul. 01, 2024
Guarantor Obligations [Line Items]
Assets held-in-trust		$ 948,500,000		$ 944,600,000
Collateral trusts, investments and cash		588,600,000		609,300,000
Surplus notes		322,200,000		317,100,000
Interest receivable		37,700,000		18,200,000
Debt		564,600,000		530,200,000
Subsidiary - HG Global
Guarantor Obligations [Line Items]
Purchase of surplus notes				$ 503,000,000.0
Percentage of risk premium ceded				60.00%
Renegotiation period				5 years
Percent over a target trust balance				102.00%
Subsidiary - HG Global | Regulation 114
Guarantor Obligations [Line Items]
Assets held-in-trust		341,600,000		$ 340,200,000
Supplement trust target				603,000,000
Subsidiary - HG Global | Supplemental Trust
Guarantor Obligations [Line Items]
Assets held-in-trust		606,900,000		604,400,000
Variable Interest Entity, Primary Beneficiary - Build America Mutual Assurance Company | Fidus Re Ltd.
Guarantor Obligations [Line Items]
Issuance of insurance linked securities						$ 150,000,000	$ 150,000,000	$ 100,000,000
Insurance-linked securities, term						12 years	12 years	12 years
Insurance-linked securities, callable term						7 years	5 years	5 years
Percentage of par value of policy reinsured						90.00%	90.00%	90.00%
Reinsurance, limit on total reimbursement						$ 150,000,000	$ 150,000,000	$ 100,000,000
Reinsured amount				$ 125,000,000
2018 Covered Portfolio | Variable Interest Entity, Primary Beneficiary - Build America Mutual Assurance Company | Fidus Re Ltd.
Guarantor Obligations [Line Items]
Percentage of financial guaranty policies covered				20.00%
2021 Covered Portfolio | Variable Interest Entity, Primary Beneficiary - Build America Mutual Assurance Company | Fidus Re Ltd.
Guarantor Obligations [Line Items]
Percentage of financial guaranty policies covered				25.00%
2022 Covered Portfolio | Variable Interest Entity, Primary Beneficiary - Build America Mutual Assurance Company | Fidus Re Ltd.
Guarantor Obligations [Line Items]
Percentage of financial guaranty policies covered				27.00%
BAM Surplus Notes | Surplus Notes
Guarantor Obligations [Line Items]
Basis spread on variable rate				3.00%
Interest rate				8.20%
Repayments of unsecured debt	$ 8,000,000	27,400,000	$ 0		$ 0
Accrued interest payment held in trust	300,000	2,000,000
Repayment of principal	5,100,000	17,800,000
Accrued interest payment held outside of trust	$ 2,600,000	7,600,000
Debt		322,200,000		$ 317,100,000
Interest receivable		$ 174,500,000		$ 184,800,000
BAM Surplus Notes | Surplus Notes | Subsequent Event
Guarantor Obligations [Line Items]
Interest rate									10.00%
Maximum | Fidus Re Ltd.
Guarantor Obligations [Line Items]
Reinsurance, maximum amount reinsured						276,700,000	301,700,000	276,100,000
Maximum | Subsidiary - HG Global
Guarantor Obligations [Line Items]
Percentage of par value of policy reinsured				15.00%
Minimum | Fidus Re Ltd.
Guarantor Obligations [Line Items]
Reinsurance obligation						$ 110,000,000	$ 135,000,000	$ 165,000,000