Loss and Loss Adjustment Expenses - Summary Exposures to Various Asbestos Related Claims (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Asbestos Claims [Line Items]
Balance, beginning of period	$ 745,278	$ 760,561	$ 772,887
Incurred losses and LAE during the current year	152,316	160,798	157,226
Loss and LAE payments	(50,954)	(52,292)	(50,113)
Balance, end of period	696,037	745,278	760,561
Asbestos Issue [Member]
Asbestos Claims [Line Items]
Balance, beginning of period	260	318	1,323
Incurred losses and LAE during the current year	(2)	(44)	(936)
Loss and LAE payments	(10)	(14)	(69)
Balance, end of period	$ 248	$ 260	$ 318