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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Operating Income		$ 44,623	$ 41,065	$ 84,627	$ 70,803
Business restructuring		(225)	(450)	(582)	(1,183)
Interest expense, net		(1,259)	(1,766)	(2,489)	(3,619)
Other, net		4,437	235	1,175	3,380
Income Before Provision for Income Taxes		47,801	39,534	83,313	70,564
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Income		67,256	60,828	114,912	113,231
Operating Segments [Member] | Surfactants [Member]
Segment Reporting Information [Line Items]
Operating Income		48,503	32,086	84,659	69,253
Operating Segments [Member] | Polymers [Member]
Segment Reporting Information [Line Items]
Operating Income		15,527	22,760	23,043	34,865
Operating Segments [Member] | Specialty Products [Member]
Segment Reporting Information [Line Items]
Operating Income		3,226	5,982	7,210	9,113
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Unallocated corporate expenses	[1]	$ (22,408)	$ (19,313)	$ (29,703)	$ (41,245)

[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.