Segment Reporting - Operating Segment (Detail) - USD ($) $ in Thousands		3 Months Ended													12 Months Ended
		Dec. 31, 2019		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Segment Reporting Information [Line Items]
Net sales		$ 444,990		$ 451,582	$ 473,003	$ 489,170	$ 466,659		$ 507,997		$ 519,866		$ 499,335		$ 1,858,745	[1]	$ 1,993,857	[1]	$ 1,925,007	[1]
Operating income		28,491		$ 27,966	$ 41,065	$ 29,738	35,451	[2]	$ 27,145	[2]	$ 45,386	[2]	$ 41,283	[2]	127,260	[3]	149,265	[2],[3]	154,840	[3]
Assets		1,579,367	[4]				1,514,614	[4]							1,579,367	[4]	1,514,614	[4]	1,502,892
Capital expenditures															105,572		86,647		78,613
Depreciation and amortization expenses															78,701		81,115		79,022
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales															1,858,745		1,993,857		1,925,007
Operating income	[5]														208,762		211,552		221,422
Assets		1,331,929					1,285,200								1,331,929		1,285,200		1,311,932
Capital expenditures															103,354		84,398		75,780
Depreciation and amortization expenses															76,056		78,917		77,119
Surfactants [Member]
Segment Reporting Information [Line Items]
Net sales															1,272,723		1,385,932		1,297,555
Surfactants [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales															1,272,723		1,385,932		1,297,555
Operating income															122,780		133,518	[5]	125,712	[5]
Assets		907,032					850,553								907,032		850,553		881,415
Capital expenditures															69,725		51,543		50,400
Depreciation and amortization expenses															48,422		50,514		49,102
Polymers [Member]
Segment Reporting Information [Line Items]
Net sales															512,347		527,420		546,634
Polymers [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales															512,347		527,420		546,634
Operating income															69,567		66,373	[5]	85,745	[5]
Assets		338,179					351,690								338,179		351,690		355,065
Capital expenditures															29,188		26,663		21,146
Depreciation and amortization expenses															22,151		23,253		22,998
Specialty Products [Member]
Segment Reporting Information [Line Items]
Net sales															73,675		80,505		80,818
Specialty Products [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales															73,675		80,505		80,818
Operating income															16,415		11,661	[5]	9,965	[5]
Assets		$ 86,718					$ 82,957								86,718		82,957		75,452
Capital expenditures															4,441		6,192		4,234
Depreciation and amortization expenses															$ 5,483		$ 5,150		$ 5,019

[1] Net sales are attributed to countries based on the location of the Company facility making the sales.

[2] The 2018 amounts for the noted line items have been retrospectively changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from LIFO to FIFO

[3] The 2018 and 2017 amounts for the noted line items have been retrospectively changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from LIFO to FIFO.

[4] The 2018 amounts for the noted line items have been retrospectively changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from LIFO to FIFO.

[5] The 2018 and 2017 amounts for the noted line items have been retrospectively changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from LIFO to FIFO