Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 137,804	$ 126,770	$ 103,129
Weighted-average number of shares outstanding		22,922	22,949	23,054
Basic earnings per share		$ 6.01	$ 5.52	$ 4.47
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 137,804	$ 126,770	$ 103,129
Weighted-average number of shares outstanding		22,922	22,949	23,054
Add weighted-average net shares related to unvested stock awards (under treasury share method)		1	1	2
Weighted-average shares applicable to diluted earnings		23,287	23,256	23,316
Diluted earnings per share		$ 5.92	$ 5.45	$ 4.42
Stock Option [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)	[1]	138	112	97
Stock Appreciation Rights (SARs) [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)		166	145	125
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)		60	49	38

[1] Options/SARs to purchase 103,182, 127,434 and 107,125 shares of common stock were excluded from the computations of diluted earnings per share for the years ended December 31, 2021, 2020 and 2019, respectively. The options’/SARs’ exercise prices were greater than the average market price for the common stock and inclusion of the instruments would have had an antidilutive effect on the computations of the earnings per share.