Earnings Per Share - Computations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 20,427	$ 24,912	$ 75,946	$ 63,096
Weighted-average number of common shares outstanding		22,819	22,732	22,771	22,731
Basic earnings per share		$ 0.90	$ 1.10	$ 3.34	$ 2.78
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 20,427	$ 24,912	$ 75,946	$ 63,096
Weighted-average number of common shares outstanding		22,819	22,732	22,771	22,731
Add weighted-average net shares issuable from assumed exercise of options (under treasury stock method)	[1]	134	119	124	117
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		6	2	5	3
Weighted-average shares applicable to diluted earnings		23,082	22,853	22,975	22,851
Diluted earnings per share		$ 0.89	$ 1.09	$ 3.31	$ 2.76
Stock Appreciation Rights (SARs) [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares issuable from assumed exercise of options (under treasury stock method)		73	0	40	0
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares issuable from assumed exercise of options (under treasury stock method)		50	0	35	0

[1] Options to purchase 58,287 shares of Company common stock were excluded from the computations of diluted earnings per share for the nine months ended September 30, 2016. Options to purchase 90,734 and 136,170 shares of Company common stock were excluded from the computations of diluted earnings per share for the three and nine months ended September 30, 2015, respectively. The excluded options’ exercise prices were greater than the average market price for the common stock, and their effect would have been antidilutive.