Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,741	$ 1,708	$ 5,200	$ 5,111
Expected return on plan assets	(2,251)	(2,398)	(6,759)	(7,184)
Amortization of net actuarial loss	776	1,103	2,540	3,401
Net periodic benefit (income) cost	266	413	981	1,328
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	177	200	564	593
Expected return on plan assets	(218)	(268)	(694)	(795)
Amortization of net actuarial loss	18	46	58	137
Net periodic benefit (income) cost	$ (23)	$ (22)	$ (72)	$ (65)