Postretirement Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net actuarial (gain) loss	$ (1,110)	$ 35,999	$ (18,539)
Amortization of net actuarial loss	(4,534)	(2,687)	(5,109)
Total recognized in other comprehensive income	(5,644)	33,312	(23,648)
Total recognized in net periodic benefit cost and other comprehensive income	(3,874)	33,412	(20,943)
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net actuarial (gain) loss	(781)	2,577	(3,264)
Amortization of net actuarial loss	(179)		(288)
Total recognized in other comprehensive income	(960)	2,577	(3,552)
Total recognized in net periodic benefit cost and other comprehensive income	$ (1,046)	$ 2,238	$ (3,306)