Segment Reporting - Operating Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Net sales	$ 454,231	$ 491,429	$ 504,111	$ 477,442	$ 474,329	$ 475,466	$ 474,445	$ 456,546	$ 1,927,213	[1]	$ 1,880,786	[1]	$ 1,803,737	[1]
Operating income	9,004	22,253	36,914	22,523	13,905	31,085	35,869	28,294	90,694		109,153		128,716
Assets	1,162,014				1,167,202				1,162,014		1,167,202		985,478
Capital expenditures									101,819		92,865		83,159
Depreciation and amortization expenses									63,804		56,400		51,294
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									1,927,213		1,880,786		1,803,737
Operating income									131,955		165,639		178,963
Assets	1,129,905				1,070,949				1,129,905		1,070,949		950,714
Capital expenditures									98,823		91,440		81,317
Depreciation and amortization expenses									62,708		55,382		49,634
Surfactants [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									1,296,638		1,317,164		1,305,800
Operating income									60,778		100,201		118,591
Assets	741,677				710,521				741,677		710,521		692,891
Capital expenditures									70,796		66,266		56,236
Depreciation and amortization expenses									41,483		36,400		34,036
Polymers [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									550,966		483,361		423,959
Operating income									60,690		54,536		48,130
Assets	320,640				292,015				320,640		292,015		199,013
Capital expenditures									22,409		18,804		19,266
Depreciation and amortization expenses									18,433		16,351		13,328
Specialty Products [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									79,609		80,261		73,978
Operating income									10,487		10,902		12,242
Assets	67,588				68,413				67,588		68,413		58,810
Capital expenditures									5,618		6,370		5,815
Depreciation and amortization expenses									$ 2,792		$ 2,631		$ 2,270

[1] Net sales are attributed to countries based on selling location.