Segment Reporting - Reconciliation of Segment Information to Income Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Operating Income		$ 42,395	$ 27,966	$ 127,022	$ 98,769
Business restructuring		(126)	(459)	(708)	(1,642)
Interest expense, net		(1,626)	(1,402)	(4,115)	(5,021)
Other, net		2,629	885	3,804	4,265
Income Before Provision for Income Taxes		43,398	27,449	126,711	98,013
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Income		65,131	45,204	180,043	158,435
Operating Segments [Member] | Surfactants [Member]
Segment Reporting Information [Line Items]
Operating Income		41,151	19,660	125,810	88,913
Operating Segments [Member] | Polymers [Member]
Segment Reporting Information [Line Items]
Operating Income		22,387	23,283	45,430	58,148
Operating Segments [Member] | Specialty Products [Member]
Segment Reporting Information [Line Items]
Operating Income		1,593	2,261	8,803	11,374
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Unallocated corporate expenses	[1]	$ (22,610)	$ (16,779)	$ (52,313)	$ (58,024)

[1] 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.