Reserve for Losses and Loss Adjustment Expenses - Activity in the Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Summary of reserve for losses and loss adjustment expenses
Balance, beginning of year	$ 3,401,281	$ 3,471,147	$ 3,579,940
Less reinsurance recoverables on unpaid losses and loss adjustment expenses	445,573	431,889	451,741
Net balance, beginning of year	2,955,708	3,039,258	3,128,199
Net losses:
Current year	779,650	794,848	813,515
(Favorable) Unfavorable development of reserves established in prior years, net	(40,215)	5,646	(36,753)
Total	739,435	800,494	776,762
Paid related to:
Current year	(113,268)	(101,996)	(108,139)
Prior years	(733,248)	(782,048)	(757,564)
Total paid	(846,516)	(884,044)	(865,703)
Net balance, end of year	2,848,627	2,955,708	3,039,258
Plus reinsurance recoverables on unpaid losses and loss adjustment expenses	409,069	445,573	431,889
Balance, end of year	3,257,696	3,401,281	3,471,147
NORCAL Group
Net losses:
Current year			4,900
(Favorable) Unfavorable development of reserves established in prior years, net	$ 5,300	$ 8,300	$ 10,800