Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,730	$ 1,702	$ 3,459	$ 3,403
Expected return on plan assets	(2,254)	(2,393)	(4,508)	(4,786)
Amortization of net actuarial loss	882	1,149	1,764	2,298
Net periodic benefit (income) cost	358	458	715	915
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	194	198	387	393
Expected return on plan assets	(238)	(265)	(476)	(527)
Amortization of net actuarial loss	20	46	40	91
Net periodic benefit (income) cost	$ (24)	$ (21)	$ (49)	$ (43)