Earnings Per Share - Computations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 27,654	$ 21,270
Weighted-average number of common shares outstanding		22,733	22,718
Basic earnings per share		$ 1.22	$ 0.94
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 27,654	$ 21,270
Weighted-average number of common shares outstanding		22,733	22,718
Add weighted-average net shares from assumed exercise of options (under treasury stock method)	[1]	113	104
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		4	5
Weighted-average shares applicable to diluted earnings		22,882	22,827
Diluted earnings per share		$ 1.21	$ 0.93
Stock Appreciation Rights (SARs) [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)		8
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)		24

[1] Options to purchase 89,617 and 226,098 shares of Company common stock were excluded from the computations of diluted earnings per share for the three months ended March 31, 2016 and March 31, 2015, respectively. The options’ exercise prices were greater than the average market price for the common stock, and the effect of including the options would have been antidilutive.