Pension and Other Postretirement Benefits - Summary of Changes in the Fair Value of the Level 3 Plan Assets for U.S. and Foreign Pension Plans (Detail) £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 GBP (£)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	$ 48,055	£ 38,955
Voluntary contributions made	1,521		$ 1,522	$ 1,715
Fair value of plan assets, Ending balance	56,419	£ 41,820	48,055
Defined Benefit Pension Plan [Member] | U.S. Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	188,722
Fair value of plan assets, Ending balance	199,138		188,722
Defined Benefit Pension Plan [Member] | U.S. Defined Benefit Pension Plans [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	188,722		139,376
Voluntary contributions made	403		376
Change in net unrealized (losses) gains	13,825		(160)
Other, primarily impact from changes in foreign currency exchange rates	0		0
Fair value of plan assets, Ending balance	199,138		188,722	139,376
Defined Benefit Pension Plan [Member] | Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	48,055		49,628
Voluntary contributions made	1,979		1,687
Change in net unrealized (losses) gains	(7,954)		8,869
Other, primarily impact from changes in foreign currency exchange rates	4,673		(8,930)
Fair value of plan assets, Ending balance	56,419		48,055	49,628
Significant Unobservable Inputs (Level 3) [Member] | Defined Benefit Pension Plan [Member] | U.S. Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	33,830
Fair value of plan assets, Ending balance	51,061		33,830
Significant Unobservable Inputs (Level 3) [Member] | Defined Benefit Pension Plan [Member] | U.S. Defined Benefit Pension Plans [Member] | U.S. [Member] | Hedge and Absolute Return Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	0		4,967
Withdrawals			(4,967)
Realized gains (losses)			0
Change in net unrealized (losses) gains			0
Other, primarily impact from changes in foreign currency exchange rates			0
Fair value of plan assets, Ending balance			0	4,967
Significant Unobservable Inputs (Level 3) [Member] | Defined Benefit Pension Plan [Member] | U.S. Defined Benefit Pension Plans [Member] | U.S. [Member] | Managed Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	33,830		32,210
Voluntary contributions made	16,000
Withdrawals	(5,364)		0
Realized gains (losses)	1,304		1,857
Change in net unrealized (losses) gains	4,068		(237)
Other, primarily impact from changes in foreign currency exchange rates	0		0
Fair value of plan assets, Ending balance	49,838		33,830	32,210
Significant Unobservable Inputs (Level 3) [Member] | Defined Benefit Pension Plan [Member] | Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	8,593		10,571
Voluntary contributions made	0
Withdrawals	0		0
Realized gains (losses)	0		0
Change in net unrealized (losses) gains	229		(280)
Other, primarily impact from changes in foreign currency exchange rates	815		(1,698)
Fair value of plan assets, Ending balance	$ 9,637		$ 8,593	$ 10,571