Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 351	$ 1,215	$ 1,035
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	6,616	6,194	6,651
Expected return on plan assets	(9,450)	(9,284)	(9,288)
Amortization of net actuarial loss	2,490	3,814	3,085
Net periodic benefit cost	(344)	724	448
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	554	565	592
Expected return on plan assets	(787)	(885)	(797)
Amortization of net actuarial loss	244	219	382
Net periodic benefit cost	$ 11	$ (101)	$ 177