Selected Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, 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
Quarterly Financial Information Disclosure [Abstract]
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]
Gross Profit	49,851	65,099	71,589	63,024	60,937	74,341	73,707	72,700	249,563		281,685		291,553
Operating Income	9,004	22,253	36,914	22,523	13,905	31,085	35,869	28,294	90,694		109,153		128,716
Interest, net	(2,617)	(2,846)	(3,021)	(2,957)	(2,863)	(2,987)	(2,329)	(2,179)	(11,441)		(10,358)		(9,599)
Income Before Income Taxes	6,012	18,228	33,206	18,089	10,310	27,847	32,200	25,273	75,535		95,630		115,722
Net Income	6,225	13,480	24,368	13,008	10,537	20,149	22,654	18,997	57,081		72,337		79,687
Net Income Attributable to Stepan Company	$ 6,239	$ 13,491	$ 24,353	$ 13,018	$ 10,650	$ 20,402	$ 22,742	$ 19,034	$ 57,101		$ 72,828		$ 79,396
Diluted earnings per share	$ 0.27	$ 0.59	$ 1.06	$ 0.57	$ 0.46	$ 0.89	$ 0.99	$ 0.83	$ 2.49		$ 3.18		$ 3.49

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