Reserve for Losses and Loss Adjustment Expenses - Reconciliation of Claims Development (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	$ 2,606,166
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	409,069	$ 445,573	$ 431,889	$ 451,741
Reserve for the future utilization of the DDR benefit	101,151
Unallocated loss adjustment expenses	120,965
Annual Aggregate Deductible	8,965
Loss portfolio transfers	1,592
Purchase accounting adjustments	9,783
Other	5
Liability for unpaid claims and claim adjustment expense	242,461
Gross liability for losses and loss adjustment expenses	3,257,696	$ 3,401,281	$ 3,471,147	$ 3,579,940
Medical Professional Liability Claims-Made
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	1,770,454
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	212,272
Medical Professional Liability Occurrence
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	408,182
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	52,524
Medical Technology Liability Claims-Made
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	56,311
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	38,197
Other short-duration lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	187,880
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	41,169
Workers' Compensation Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	141,770
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	39,118
Segregated Portfolio Cell Reinsurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	41,569
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	$ 25,789