Pension and Other Postretirement Benefits - Summary of Changes in the Fair Value of the Level 3 Plan Assets for the U.S. and Foreign Pension Benefits Plans (Detail) £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 GBP (£)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 GBP (£)
Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	$ 49,651	£ 38,991
Fair value of plan assets, Ending balance	57,900	£ 43,913	$ 49,651	£ 38,991
Defined Benefit Pension Plan [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	182,541		199,138
Fair value of plan assets, Ending balance	195,667		182,541
Defined Benefit Pension Plan [Member] | Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	49,651		56,419
Fair value of plan assets, Ending balance	57,900		49,651
Defined Benefit Pension Plan [Member] | Alternative Investments [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	23,673
Fair value of plan assets, Ending balance	19,341		23,673
Defined Benefit Pension Plan [Member] | Alternative Investments, Absolute Return Funds [Member] | Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	7,569
Fair value of plan assets, Ending balance	6,495		7,569
Defined Benefit Pension Plan [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	23,673
Fair value of plan assets, Ending balance	19,275		23,673
Defined Benefit Pension Plan [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	7,569
Fair value of plan assets, Ending balance	6,495		7,569
Defined Benefit Pension Plan [Member] | Significant Unobservable Inputs (Level 3) [Member] | Alternative Investments [Member] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	$ 23,673		$ 49,838
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
Withdrawals	$ (4,921)		$ (26,131)
Realized gains (losses)	1,445		9,061
Change in net unrealized (losses) gains	(856)		(9,095)
Other, primarily impact from changes in foreign currency exchange rates	0		0
Fair value of plan assets, Ending balance	19,341		23,673
Defined Benefit Pension Plan [Member] | Significant Unobservable Inputs (Level 3) [Member] | Alternative Investments, Absolute Return Funds [Member] | Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, Beginning balance	$ 7,569		$ 9,637
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
Withdrawals	$ (1,791)		$ (1,037)
Realized gains (losses)	(701)		(436)
Change in net unrealized (losses) gains	1,189		(98)
Other, primarily impact from changes in foreign currency exchange rates	229		(497)
Fair value of plan assets, Ending balance	$ 6,495		$ 7,569