Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Computation of Basic Earnings per Share
Net income attributable to Stepan Company	$ 21,270		$ 13,018
Weighted-average number of shares outstanding	22,718		22,773
Basic earnings per share	$ 0.94		$ 0.57
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company	$ 21,270		$ 13,018
Weighted-average number of shares outstanding	22,718		22,773
Add weighted-average net shares issuable from assumed exercise of options (under treasury stock method)	104	[1]	182	[1]
Add weighted-average net shares related to unvested stock awards (under treasury stock method)	5		9
Weighted-average shares applicable to diluted earnings	22,827		22,964
Diluted earnings per share	$ 0.93		$ 0.57

[1] Options to purchase 226,098 and 47,639 shares of Company common stock were excluded from the computation of diluted earnings per share for the three months ended March 31, 2015 and March 31, 2014, respectively. The options’ exercise prices were greater than the average market price for the common stock and their effect would have been antidilutive.