Postretirement Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (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]
Net actuarial (gain) loss	$ 1,930	$ 1,570	$ (9,793)
Amortization of net actuarial gain (loss)	23	(2,277)	(4,444)
Total recognized in other comprehensive income	1,953	(707)	(14,237)
Total recognized in net periodic benefit cost and other comprehensive income	346	(2,309)	(15,470)
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net actuarial (gain) loss	135	2,430	(757)
Amortization of net actuarial gain (loss)	(334)	(9)	(129)
Total recognized in other comprehensive income	(199)	2,421	(886)
Total recognized in net periodic benefit cost and other comprehensive income	$ 109	$ 2,405	$ (720)