Pension and Other Postretirement Benefits - Contributions for Pension and Other Postretirement Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Postretirement Benefit Plans [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contributions	$ 307	$ 275
Foreign Defined Benefits Pension Plans [Member] | Defined Benefit Pension Plan [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contributions	540	424
Foreign Defined Benefits Pension Plans [Member] | Defined Benefit Pension Plan [Member] | U.K. [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contributions	91	65
U.S. Defined Benefit Pension Plans [Member] | Defined Benefit Pension Plan [Member] | U.S. [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contributions	$ 705	$ 650