Pension and Other Postretirement Benefits - Schedule of Changes in Plan Assets (Detail) £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 GBP (£)	Dec. 31, 2017 USD ($)
Foreign Pension Benefits [Member]
Change in plan assets:
Fair value of plan assets, Beginning balance	$ 56,419	£ 41,820
Corporate contributions	982		$ 1,521
Fair value of plan assets, Ending balance	49,651	£ 38,991	56,419
Defined Benefit Pension Plan [Member]
Change in plan assets:
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]
Change in plan assets:
Fair value of plan assets, Beginning balance	199,138		188,722
Actual return on plan assets	(4,765)		23,366
Foreign currency exchange rate changes	0		0
Corporate contributions	1,614		403
Participant contributions	0		0
Gross benefits paid	(13,446)		(13,353)
Fair value of plan assets, Ending balance	182,541		199,138
Defined Benefit Pension Plan [Member] | Foreign Pension Benefits [Member]
Change in plan assets:
Fair value of plan assets, Beginning balance	56,419		48,055
Actual return on plan assets	(2,477)		3,998
Foreign currency exchange rate changes	(2,991)		4,673
Corporate contributions	1,648		1,979
Participant contributions	0		0
Gross benefits paid	(2,948)		(2,286)
Fair value of plan assets, Ending balance	49,651		56,419
Other Postretirement Benefit Plans [Member]
Change in plan assets:
Fair value of plan assets, Beginning balance	0		0
Actual return on plan assets	0		0
Foreign currency exchange rate changes	0		0
Corporate contributions	1,103		1,138
Participant contributions	104		92
Gross benefits paid	(1,207)		(1,230)
Fair value of plan assets, Ending balance	$ 0		$ 0