Segment Reporting - Reconciliation of Segment Information to Income Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Operating Income	[1],[2]	$ 41,065	$ 45,386	$ 70,803	$ 86,669
Business restructuring expenses (Note 17)		(450)	(273)	(1,183)	(631)
Interest expense, net		(1,766)	(2,672)	(3,619)	(5,823)
Other, net		235	484	3,380	1,644
Income Before Provision for Income Taxes	[1],[2]	39,534	43,198	70,564	82,490
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Income	[1]	60,828	58,617	113,231	117,040
Operating Segments [Member] | Surfactants [Member]
Segment Reporting Information [Line Items]
Operating Income	[1]	32,086	34,078	69,253	75,546
Operating Segments [Member] | Polymers [Member]
Segment Reporting Information [Line Items]
Operating Income	[1]	22,760	20,299	34,865	37,604
Operating Segments [Member] | Specialty Products [Member]
Segment Reporting Information [Line Items]
Operating Income		5,982	4,240	9,113	3,890
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Unallocated corporate expenses	[3]	$ (19,313)	$ (12,958)	$ (41,245)	$ (29,740)

[1] The 2018 amounts for the noted line items have been retrospectively changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from LIFO to FIFO.

[2] The 2018 amounts for the noted line items have been retrospectively changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from the last in, first out (LIFO) basis to the first in, first out (FIFO) basis.

[3] Unallocated corporate expenses primarily comprise corporate administrative expenses (e.g., corporate finance, legal, human resources, information systems, deferred compensation and environmental remediation) that are not included in segment operating income and not used to evaluate segment performance.