Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,729	$ 1,701
Expected return on plan assets	(2,254)	(2,393)
Amortization of net actuarial loss	882	1,149
Net periodic benefit cost	357	457
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	193	195
Expected return on plan assets	(238)	(262)
Amortization of net actuarial loss	20	45
Net periodic benefit cost	$ (25)	$ (22)