Earnings Per Share - Computation 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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 16,914	$ 24,353	$ 38,184	$ 37,371
Weighted-average number of common shares outstanding		22,742	22,763	22,731	22,768
Basic earnings per share		$ 0.74	$ 1.07	$ 1.68	$ 1.64
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 16,914	$ 24,353	$ 38,184	$ 37,371
Weighted-average number of common shares outstanding		22,742	22,763	22,731	22,768
Add weighted-average net shares issuable from assumed exercise of options (under treasury stock method)	[1]	127	158	116	170
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		2	10	3	10
Weighted-average shares applicable to diluted earnings		22,871	22,931	22,850	22,948
Diluted earnings per share		$ 0.74	$ 1.06	$ 1.67	$ 1.63

[1] Options to purchase 91,678 and 158,888 shares of Company common stock were excluded from the computations of diluted earnings per share for the three and six months ended June 30, 2015, respectively. Options to purchase 103,382 and 75,511 shares of Company common stock were excluded from the computations of diluted earnings per share for the three and six months ended June 30, 2014, respectively. The options’ exercise prices were greater than the average market price for the common stock and their effect would have been antidilutive.