Insurance - Summary of Percentage Ceded to Reinsurers and Reinsurance Recoverable and Rating Levels (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered			$ 7,000
Reinsurance Recoverable, Allowance for Credit Loss	$ 106	$ 75
Reinsurance Recoverables, Gross	311,000
Unsecured Reinsurance Recoverables	200,000
Reinsurance Recoverable, Gross, All Other	126,000
Unsecured Reinsurance Recoverable, All Other	56,000
Letters of Credit Outstanding, Amount	$ 76,000
Number of Reinsurers Covering Majority	3
Percentage of Ceded Reinsurance Recoverable Represented by Top Three	59.60%
Uncollateralized Credit Exposure Supoorted by Unlimited Uncapped Indemnity	$ 38,000	44,000
Deferred Ceded Premiums And Reinsurance Recoverables	$ 553,000
Reinsurance, Reinsured Risk, Percentage	70.00%
Financial Guarantee
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Letters of Credit Outstanding, Amount	$ 39,000
Specialty Property & Casualty Program
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Letters of Credit Outstanding, Amount	37,000
Financial Guarantee
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	1,000	$ (1,000)
QBE Insurance Corporation | Property and Casualty, Commercial Insurance | Standard & Poor's, A Rating
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Reinsurance Recoverables, Gross	33,000
Unsecured Reinsurance Recoverables	33,000
Assured Guaranty Re Ltd | Financial Guarantee | Standard & Poor's, AA Rating
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Reinsurance Recoverables, Gross	23,000
Unsecured Reinsurance Recoverables	0
General Reinsurance Company | Property and Casualty, Commercial Insurance | Standard & Poor's, AA+ Rating
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Reinsurance Recoverables, Gross	129,000
Unsecured Reinsurance Recoverables	$ 111,000