Loss and Loss Adjustment Expenses - Summary Exposures to Various Asbestos Related Claims (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Asbestos Claims [Line Items]
Balance, beginning of period	$ 651,309	$ 673,994	$ 696,037
Incurred losses and LAE during the current year	169,937	157,267	148,263
Balance, end of period	613,583	651,309	673,994
Asbestos Issue [Member]
Asbestos Claims [Line Items]
Balance, beginning of period	313	310	248
Incurred losses and LAE during the current year	34	14	15
Loss and LAE payments	(7)	(11)	47
Balance, end of period	$ 340	$ 313	$ 310