Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 6,815	$ 6,936	$ 6,424
Expected return on plan assets	(9,579)	(9,523)	(8,828)
Amortization of net actuarial loss	4,534	2,687	5,109
Net periodic benefit cost	1,770	100	2,705
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	789	964	899
Expected return on plan assets	(1,054)	(1,303)	(941)
Amortization of net actuarial loss	179		288
Net periodic benefit cost	$ (86)	$ (339)	$ 246