Segment Reporting - Reconciliation of Segment Information to Consolidated Financial Statements (Detail) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	[2]	Sep. 30, 2018	Sep. 30, 2017	[2]
Segment Reporting Information [Line Items]
Operating income	[1]	$ 27,694	$ 30,434		$ 112,034	$ 115,797
Business restructuring expenses (Note 15)		(1,715)	(426)		(2,346)	(1,798)
Interest expense, net		(2,797)	(2,763)		(8,620)	(8,618)
Other, net	[1]	346	1,641		1,990	3,526
Income Before Provision for Income Taxes		25,243	29,312		105,404	110,705
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating income		51,285	44,695		165,996	163,675
Operating Segments [Member] | Surfactants [Member]
Segment Reporting Information [Line Items]
Operating income		31,201	22,559		105,670	92,080
Operating Segments [Member] | Polymers [Member]
Segment Reporting Information [Line Items]
Operating income		17,431	21,146		53,783	63,884
Operating Segments [Member] | Specialty Products [Member]
Segment Reporting Information [Line Items]
Operating income		2,653	990		6,543	7,711
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Unallocated corporate expenses	[3]	$ (21,876)	$ (13,835)		$ (51,616)	$ (46,080)

[1] The 2017 amounts for the noted line items have been immaterially changed from the amounts originally reported as a result of the Company’s first quarter 2018 adoption of Accounting Standards Update (ASU) No. 2017-7, Compensation –Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.

[2] The 2017 data has been immaterially changed from the amounts originally reported as a result of the Company’s first quarter 2018 adoption of ASU No. 2017-7, Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost

[3] Unallocated corporate expenses are primarily comprised of 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.