Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Net Sales	$ 419,291	$ 444,011	$ 452,414	$ 460,451	$ 454,231	$ 491,429	$ 504,111	$ 477,442	$ 1,776,167	[1]	$ 1,927,213	[1]	$ 1,880,786	[1]
Gross Profit	74,689	77,598	79,512	76,442	49,851	65,099	71,589	63,024	308,241		249,563		281,685
Operating income	20,223	38,794	28,595	35,178	9,004	22,253	36,914	22,523	122,790		90,694		109,153
Interest, net	(3,773)	(3,837)	(2,869)	(4,054)	(2,617)	(2,846)	(3,021)	(2,957)	(14,533)		(11,441)		(10,358)
Income Before Income Taxes	15,061	33,113	24,146	30,536	6,012	18,228	33,206	18,089	102,856		75,535		95,630
Net Income	12,876	24,934	16,941	21,286	6,225	13,480	24,368	13,008	76,037		57,081		72,337
Net Income Attributable to Stepan Company	$ 12,872	$ 24,912	$ 16,914	$ 21,270	$ 6,239	$ 13,491	$ 24,353	$ 13,018	$ 75,968		$ 57,101		$ 72,828
Diluted earnings per share	$ 0.56	$ 1.09	$ 0.74	$ 0.93	$ 0.27	$ 0.59	$ 1.06	$ 0.57	$ 3.32		$ 2.49		$ 3.18

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