Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,702	$ 1,723	$ 3,403	$ 3,446
Expected return on plan assets	(2,393)	(2,378)	(4,786)	(4,756)
Amortization of net actuarial loss	1,149	661	2,298	1,323
Net periodic benefit (income) cost	458	6	915	13
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	198	247	393	490
Expected return on plan assets	(265)	(333)	(527)	(661)
Amortization of net actuarial loss	46		91
Net periodic benefit (income) cost	$ (21)	$ (86)	$ (43)	$ (171)