Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 6,934	$ 6,815	$ 6,936
Expected return on plan assets	(9,012)	(9,579)	(9,523)
Amortization of net actuarial loss	3,386	4,534	2,687
Net periodic benefit cost	1,308	1,770	100
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	733	789	964
Expected return on plan assets	(900)	(1,054)	(1,303)
Amortization of net actuarial loss	77	179
Net periodic benefit cost	$ (90)	$ (86)	$ (339)