Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 12,872	$ 24,912	$ 16,914	$ 21,270	$ 6,239	$ 13,491	$ 24,353	$ 13,018	$ 75,968	$ 57,101	$ 72,828
Deduct dividends on preferred stock												43
Income applicable to common stock										$ 75,968	$ 57,101	$ 72,871
Weighted-average number of shares outstanding										22,730	22,758	22,621
Basic earnings per share										$ 3.34	$ 2.51	$ 3.22
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company										$ 75,968	$ 57,101	$ 72,828
Weighted-average number of shares outstanding										22,730	22,758	22,621
Add weighted-average net shares from assumed exercise (under treasury share method)	[1]									118	148	215
Add weighted-average net shares related to unvested stock awards (under treasury share method)										3	11	8
Add weighted-average shares from assumed conversion of convertible preferred stock												80
Weighted-average shares applicable to diluted earnings										22,858	22,917	22,924
Diluted earnings per share		$ 0.56	$ 1.09	$ 0.74	$ 0.93	$ 0.27	$ 0.59	$ 1.06	$ 0.57	$ 3.32	$ 2.49	$ 3.18
Stock Appreciation Rights (SARs) [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise (under treasury share method)										1
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise (under treasury share method)										6

[1] Options to purchase 124,531, 99,044 and 49,815 shares of common stock were not included in the computations of diluted earnings per share for the years ended December 31, 2015, 2014 and 2013, respectively. The options’ exercise prices were greater than the average market price for the common stock and the effect of the options on earnings per share would have been antidilutive.