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, 2016	Dec. 31, 2015	Dec. 31, 2014
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net actuarial (gain) loss	$ (11,062)	$ (1,110)	$ 35,999
Amortization of net actuarial loss	(3,386)	(4,534)	(2,687)
Total recognized in other comprehensive income	(14,448)	(5,644)	33,312
Total recognized in net periodic benefit cost and other comprehensive income	(13,140)	(3,874)	33,412
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net actuarial (gain) loss	3,756	(781)	2,577
Amortization of net actuarial loss	(77)	(179)
Total recognized in other comprehensive income	3,679	(960)	2,577
Total recognized in net periodic benefit cost and other comprehensive income	$ 3,589	$ (1,046)	$ 2,238