Segment Reporting - Reconciliation of Segment Information to Consolidated Financial Statements (Detail) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	[2]	Jun. 30, 2018	Jun. 30, 2017	[2]
Segment Reporting Information [Line Items]
Operating income	[1]	$ 44,685		$ 39,133		$ 84,340	$ 85,363
Business restructuring expenses (Note 15)		(273)	$ (358)	(586)		(631)	(1,372)
Interest expense, net		(2,672)		(2,863)		(5,823)	(5,855)
Other, net	[1]	484		793		1,644	1,885
Income Before Provision for Income Taxes		42,497		37,063		80,161	81,393
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating income		57,916		57,898		114,711	118,980
Operating Segments [Member] | Surfactants [Member]
Segment Reporting Information [Line Items]
Operating income		34,218		31,164		74,469	69,535
Operating Segments [Member] | Polymers [Member]
Segment Reporting Information [Line Items]
Operating income		19,458		21,283		36,352	42,708
Operating Segments [Member] | Specialty Products [Member]
Segment Reporting Information [Line Items]
Operating income		4,240		5,451		3,890	6,737
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Unallocated corporate expenses	[3]	$ (12,958)		$ (18,179)		$ (29,740)	$ (32,245)

[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 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.