Segment Reporting - Operating Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 473,823	$ 487,814	$ 495,101	$ 468,269	$ 420,636	$ 445,030	$ 454,603	$ 445,897	$ 1,925,007	[1]	$ 1,766,166	[1]	$ 1,776,167	[1]
Operating income	30,831	$ 30,309	$ 38,961	$ 46,059	9,932	$ 28,738	$ 42,916	$ 44,607	146,160		126,193		122,790
Assets	1,470,861				1,353,890				1,470,861		1,353,890		1,238,392
Capital expenditures									78,613		103,076		119,349
Depreciation and amortization expenses									79,022		74,967		66,985
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									1,925,007		1,766,166		1,776,167
Operating income									212,743		207,282		189,419
Assets	1,311,932				1,208,697				1,311,932		1,208,697		1,124,918
Capital expenditures									75,780		100,205		116,867
Depreciation and amortization expenses									77,119		73,122		65,322
Surfactants [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									1,297,555		1,181,563		1,205,849
Operating income									119,990		99,796		104,080
Assets	881,415				831,324				881,415		831,324		758,524
Capital expenditures									50,400		64,121		79,171
Depreciation and amortization expenses									49,102		48,643		42,122
Polymers [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									546,634		498,826		491,488
Operating income									82,801		96,788		80,942
Assets	355,065				301,890				355,065		301,890		293,790
Capital expenditures									21,146		31,890		31,309
Depreciation and amortization expenses									22,998		20,275		19,541
Specialty Products [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									80,818		85,777		78,830
Operating income									9,952		10,698		4,397
Assets	$ 75,452				$ 75,483				75,452		75,483		72,604
Capital expenditures									4,234		4,194		6,387
Depreciation and amortization expenses									$ 5,019		$ 4,204		$ 3,659

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