Earnings Per Share - Computation 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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 24,912	$ 13,491	$ 63,096	$ 50,862
Weighted-average number of common shares outstanding		22,732	22,726	22,731	22,754
Basic earnings per share		$ 1.10	$ 0.59	$ 2.78	$ 2.24
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 24,912	$ 13,491	$ 63,096	$ 50,862
Weighted-average number of common shares outstanding		22,732	22,726	22,731	22,754
Add weighted-average net shares issuable from assumed exercise of options (under treasury stock method)	[1]	119	138	117	159
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		2	11	3	10
Weighted-average shares applicable to diluted earnings		22,853	22,875	22,851	22,923
Diluted earnings per share		$ 1.09	$ 0.59	$ 2.76	$ 2.22

[1] 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. Options to purchase 96,999 and 82,673 shares of Company common stock were excluded from the computations of diluted earnings per share for the three and nine months ended September 30, 2014, respectively. The options’ exercise prices were greater than the average market price for the common stock, and the effect of including the options would have been antidilutive.