Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,708	$ 1,756	$ 5,111	$ 5,202
Expected return on plan assets	(2,398)	(2,386)	(7,184)	(7,142)
Amortization of net actuarial loss	1,103	692	3,401	2,015
Net periodic benefit (income) cost	413	62	1,328	75
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	200	245	593	735
Expected return on plan assets	(268)	(330)	(795)	(991)
Amortization of net actuarial loss	46		137
Net periodic benefit (income) cost	$ (22)	$ (85)	$ (65)	$ (256)