Pension and Other Postretirement Benefits - Contributions for Pension and Other Postretirement Benefits (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Pension Plan [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contribution	$ 93	$ 540
Other Postretirement Benefit Plans [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contribution	266	307
U.S. [Member] | Defined Benefit Pension Plan [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contribution	253	0
U.S. [Member] | Defined Contribution Plan [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contribution	625	705
U.K. [Member] | Defined Benefit Pension Plan [Member]
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Contribution	$ 85	$ 91