Related-Party Transactions - Schedule (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Related Party Transaction [Line Items]
Written premiums ceded	$ 713,766	$ 626,330	$ 1,325,186	$ 1,176,966
Ceded commissions and brokerage	156,093	135,919	309,041	275,523
Due to reinsurers	646,261		646,261		$ 615,781
Due from reinsurers (net of allowance for expected credit losses of $6,808 and $6,378 at June 30, 2026 and December 31, 2025, respectively)	3,643,933		3,643,933		3,543,013
Nonrelated Party \| Lifson Re
Related Party Transaction [Line Items]
Due to reinsurers	135,367		135,367		118,788
Due from reinsurers (net of allowance for expected credit losses of $6,808 and $6,378 at June 30, 2026 and December 31, 2025, respectively)	615,317		615,317		$ 537,366
Nonrelated Party \| Lifson Re \| Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments \| Reinsurer Concentration Risk
Related Party Transaction [Line Items]
Written premiums ceded	148,571	140,363	267,088	246,500
Ceded commissions and brokerage	34,442	$ 35,656	68,367	$ 66,080
Nonrelated Party \| Mitsui Sumitomo Insurance Co., Ltd. \| Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments \| Reinsurer Concentration Risk
Related Party Transaction [Line Items]
Written premiums ceded	19,000		34,000
Ceded commissions and brokerage	4,000		7,000
Due from reinsurers	69,000		69,000
Due to reinsurers	$ 13,000		$ 13,000

Amount of commission revenue from buying and selling securities on behalf of customers.

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