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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Operating Income		$ 56,657	$ 44,623	$ 110,571	$ 84,627
Business restructuring		(114)	(225)	(195)	(582)
Other Income (Expense)
Interest, net		(1,567)	(1,259)	(3,091)	(2,489)
Other, net		2,758	4,437	3,504	1,175
Income before provision for income taxes		57,848	47,801	110,984	83,313
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Income		75,898	67,256	149,692	114,912
Operating Segments [Member] | Surfactants [Member]
Segment Reporting Information [Line Items]
Operating Income		45,896	48,503	99,106	84,659
Operating Segments [Member] | Polymers [Member]
Segment Reporting Information [Line Items]
Operating Income		23,025	15,527	40,976	23,043
Operating Segments [Member] | Specialty Products [Member]
Segment Reporting Information [Line Items]
Operating Income		6,977	3,226	9,610	7,210
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Unallocated corporate expenses	[1]	$ (19,127)	$ (22,408)	$ (38,926)	$ (29,703)

[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.