Pension and Other Postretirement Benefits - Net Periodic Pension and Other Postretirement Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
U.S. Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 537	$ 921	$ 2,207	$ 2,762
Interest cost	1,971	2,190	6,019	6,571
Expected return on plan assets	(2,752)	(2,686)	(8,244)	(8,060)
Amortization of prior service cost	78	213	293	640
Amortization of actuarial loss	1,315	1,046	4,124	3,138
Curtailment charge	0	0	1,217	0
Net benefit cost	1,149	1,684	5,616	5,051
U.K. Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	602	679	1,803	2,048
Expected return on plan assets	(674)	(795)	(2,019)	(2,399)
Amortization of actuarial loss	212	151	636	455
Net benefit cost	140	35	420	104
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	96	90	288	415
Interest cost	118	138	355	550
Amortization of prior service cost	(168)	(168)	(504)	(274)
Amortization of actuarial loss	7	47	20	57
Net benefit cost	$ 53	$ 107	$ 159	$ 748