Business Restructuring - Additional Information (Detail)	3 Months Ended			12 Months Ended
	Mar. 31, 2019 USD ($) Employees	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)
Restructuring Cost And Reserve [Line Items]
Business restructuring	$ 733,000	$ 358,000
Netherlands [Member]
Restructuring Cost And Reserve [Line Items]
Number positions eliminated | Employees	5
Severance costs	$ 396,000
Germany [Member] | Surfactants [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs	1,591,000
Germany [Member] | Surfactants [Member] | Asset and Spare Part [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs				$ 1,404,000
Fieldsboro, NJ [Member]
Restructuring Cost And Reserve [Line Items]
Business restructuring	251,000		$ 915,000
Longford Mills [Member]
Restructuring Cost And Reserve [Line Items]
Business restructuring	$ 322,000
Longford Mills [Member] | Surfactants [Member]
Restructuring Cost And Reserve [Line Items]
Number positions eliminated | Employees	30
Business restructuring	$ 6,346,000
Termination Benefits [Member] | Netherlands [Member]
Restructuring Cost And Reserve [Line Items]
Business restructuring	79,000
Termination Benefits [Member] | Longford Mills [Member] | Surfactants [Member]
Restructuring Cost And Reserve [Line Items]
Business restructuring	1,594,000
Decommissioning Costs [Member] | Germany [Member] | Surfactants [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring costs	187,000
Other Expense [Member] | Longford Mills [Member]
Restructuring Cost And Reserve [Line Items]
Business restructuring	322,000
Other Expense [Member] | Longford Mills [Member] | Surfactants [Member]
Restructuring Cost And Reserve [Line Items]
Business restructuring	$ 4,752,000