Earnings Per Share - Computations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Computation of Basic Earnings per Share
Net income attributable to Stepan Company	[1]	$ 27,882	$ 28,496	$ 59,795	$ 56,412
Weighted-average number of common shares outstanding		22,953	22,760	22,927	22,746
Basic earnings per share	[1]	$ 1.21	$ 1.25	$ 2.61	$ 2.48
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 27,882	$ 28,496	$ 59,795	$ 56,412
Weighted-average number of common shares outstanding		22,953	22,760	22,927	22,746
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		8	6	8	5
Weighted-average shares applicable to diluted earnings	[1]	23,381	23,004	23,356	22,950
Diluted earnings per share	[1]	$ 1.19	$ 1.24	$ 2.56	$ 2.46
Options [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares issuable from assumed exercise of options, SARS and contingently issuable net shares related to performance stock awards (under treasury stock method)	[2]	172	159	177	146
Stock Appreciation Rights (SARs) [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares issuable from assumed exercise of options, SARS and contingently issuable net shares related to performance stock awards (under treasury stock method)	[2]	143	41	143	20
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares issuable from assumed exercise of options, SARS and contingently issuable net shares related to performance stock awards (under treasury stock method)		105	38	101	33

[1] The 2016 amounts for the noted 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. 2016-9, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.

[2] Options/SARs to acquire 37,261 shares of Company common stock were excluded from the computations of diluted earnings per share for the six months ended June 30, 2017. Options/SARs to acquire 85,243 and 87,430 shares of Company common stock were excluded from the computations of diluted earnings per share for the three and six months ended June 30, 2016, respectively. Inclusion of the instruments would have had antidilutive effects on the computations of earnings per share.