Reinsurance Recoverables After Allowance for Credit Losses (Detail) - USD ($) $ in Thousands		Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Insurance [Abstract]
Reinsurance recoverables on paid losses		$ 128,500		$ 173,100
Ceded outstanding loss and LAE	[1]	2,038,800		2,026,100	$ 1,757,400		$ 1,703,700
Reinsurance recoverables, before allowance for credit losses		2,167,300		2,199,200
Allowance for credit losses		(5,900)	$ (2,700)	(3,200)	$ (2,600)	$ (6,000)	$ (7,900)
Total		$ 2,161,436		$ 2,195,975

[1] Reinsurance recoverables in this table include only ceded loss and LAE reserves.