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, 2017	Mar. 31, 2016
Computation of Basic Earnings per Share
Net income attributable to Stepan Company	[1]	$ 31,913	$ 27,916
Weighted-average number of common shares outstanding		22,901	22,733
Basic earnings per share	[1]	$ 1.39	$ 1.23
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 31,913	$ 27,916
Weighted-average number of common shares outstanding		22,901	22,733
Add weighted-average net shares from assumed exercise of options (under treasury stock method)	[2]	183	133
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		8	4
Weighted-average shares applicable to diluted earnings	[1]	23,331	22,899
Diluted earnings per share	[1]	$ 1.37	$ 1.22
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)	[2]	142
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)		97	29

[1] The 2016 amounts for the noted line items have been immaterially changed from the amounts originally reported as a result of the Company’s fourth quarter 2016 adoption of Accounting Standards Update (ASU) No. 2019-9, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.

[2] Options/SARs to acquire 74,521 and 89,617 shares of Company common stock were excluded from the computations of diluted earnings per share for the three months ended March 31, 2017 and March 31, 2016, because the effect of including the instruments would have been antidilutive.