Postretirement Benefit Plans - Obligations and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	$ 130,467	$ 174,863
Interest cost	6,949	4,923	$ 4,671
Actuarial (income) loss	3,634	(40,420)
Benefits paid	(9,267)	(8,899)
Benefit obligation at end of year	131,783	130,467	174,863
Fair value of plan assets at beginning of year	136,744	178,574
Actual return on plan assets	10,237	(33,187)
Employer contributions	271	256
Benefits paid	(9,267)	(8,899)
Fair value of plan assets at end of year	137,985	136,744	178,574
Over funded status at end of year	6,202	6,277
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	13,286	23,276
Interest cost	669	374	357
Actuarial (income) loss	(92)	(7,333)
Benefits paid	(804)	(709)
Foreign exchange impact	691	(2,322)
Benefit obligation at end of year	13,750	13,286	23,276
Fair value of plan assets at beginning of year	15,163	27,464
Actual return on plan assets	470	(9,393)
Employer contributions	464	536
Benefits paid	(804)	(709)
Foreign exchange impact	798	(2,735)
Fair value of plan assets at end of year	16,091	15,163	$ 27,464
Over funded status at end of year	$ 2,341	$ 1,877