Loss and Loss Adjustment Expenses - Summary Exposures to Various Asbestos Related Claims (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Asbestos Claims [Line Items]
Balance, beginning of period	$ 696,037	$ 745,278	$ 760,561
Incurred losses and LAE during the current year	148,263	152,316	160,798
Balance, end of period	673,994	696,037	745,278
Asbestos Issue [Member]
Asbestos Claims [Line Items]
Balance, beginning of period	248	260	318
Incurred losses and LAE during the current year	15	(2)	(44)
Loss and LAE payments	47	(10)	(14)
Balance, end of period	$ 310	$ 248	$ 260