Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost (income)	$ (412)	$ (329)	$ (1,239)	$ (992)
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1,651	1,731	4,954	5,193
Expected return on plan assets	(2,120)	(2,133)	(6,360)	(6,399)
Amortization of net actuarial (gain) loss	(3)	(6)	(9)	(18)
Net periodic benefit cost (income)	(472)	(408)	(1,415)	(1,224)
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	165	171	486	504
Expected return on plan assets	(187)	(177)	(552)	(522)
Amortization of net actuarial (gain) loss	82	85	242	250
Net periodic benefit cost (income)	$ 60	$ 79	$ 176	$ 232