Reinsurance - Impact of the Reinsurance Treaties on Premiums Written and Earned (Detail) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Premiums Written:
Direct													$ 762,806	$ 713,103	$ 545,441
Assumed													135,816	12,916	128,948
Gross Premium written													898,622	726,019	674,389
Premium Ceded													(269,627)	(261,144)	(199,741)
Net premiums written													628,995	464,875	474,648
Premiums Earned:
Direct													734,891	651,455	478,546
Assumed													30,621	73,261	98,498
Gross premiums earned													765,512	724,716	577,044
Ceded													(269,627)	(261,144)	(199,741)
Net premiums earned	$ 148,614	$ 122,156	$ 115,556	$ 109,559	$ 105,918	$ 106,972	$ 124,919	$ 125,763	$ 102,224	$ 94,232	$ 93,004	$ 87,843	$ 495,885	$ 463,572	$ 377,303