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, 2018 USD ($)	Dec. 31, 2018 GBP (£)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 GBP (£)
Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	$ 56,419	£ 41,820
Fair value of plan assets, Ending balance	49,651	£ 38,991	$ 56,419	£ 41,820
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	56,419
Fair value of plan assets, Ending balance	49,651		56,419
Defined Benefit Pension Plan [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	199,138		188,722
Fair value of plan assets, Ending balance	182,541		199,138
Defined Benefit Pension Plan [Member] | Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	56,419		48,055
Fair value of plan assets, Ending balance	49,651		56,419
Defined Benefit Pension Plan [Member] | Alternative Investments [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	$ 49,838		$ 33,830
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	us-gaap:FairValueInputsLevel3Member	us-gaap:FairValueInputsLevel3Member	us-gaap:FairValueInputsLevel3Member	us-gaap:FairValueInputsLevel3Member
Contributions	$ 0		$ 16,000
Withdrawals	(26,131)		(5,364)
Realized gains (losses)	9,061		1,304
Change in net unrealized (losses) gains	(9,095)		4,068
Other, primarily impact from changes in foreign currency exchange rates	0		0
Fair value of plan assets, Ending balance	23,673		49,838
Defined Benefit Pension Plan [Member] | Alternative Investments [Member] | Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	$ 9,637		$ 8,593
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	us-gaap:FairValueInputsLevel3Member	us-gaap:FairValueInputsLevel3Member	us-gaap:FairValueInputsLevel3Member	us-gaap:FairValueInputsLevel3Member
Contributions	$ 0		$ 0
Withdrawals	(1,037)		0
Realized gains (losses)	(436)		0
Change in net unrealized (losses) gains	(98)		229
Other, primarily impact from changes in foreign currency exchange rates	(497)		815
Fair value of plan assets, Ending balance	$ 7,569		$ 9,637