Significant Accounting Policies - Recognition of management fee revenue (Details)	12 Months Ended
	Dec. 31, 2024 obligation
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Management fee rate as a percent of direct and affiliated assumed written premiums of the exchange	25.00%
Performance obligations under subscriber's agreement	2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Period of time over which management fee revenue allocated to administrative services will be recognized	4 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Period of time over which management fee revenue allocated to administrative services will be recognized	4 years