Earnings Per Share - Computations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 44,809	$ 40,611
Weighted-average number of common shares outstanding		22,896	22,974
Basic earnings per share		$ 1.96	$ 1.77
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 44,809	$ 40,611
Weighted-average number of common shares outstanding		22,896	22,974
Add weighted-average net shares related to unvested stock awards (under treasury stock method)			1
Weighted-average shares applicable to diluted earnings		23,167	23,330
Diluted earnings per share		$ 1.93	$ 1.74
Stock Option [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)	[1]	99	140
Stock Appreciation Rights (SARs) [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)	[1]	120	171
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)		52	44

[1] 364,350 options/SARs to acquire shares of Company common stock were excluded from the computation of dilutive earnings per share for the three months ended March 31, 2022. Inclusion of the instruments would have had an antidilutive effect on the computations of the earnings per share. No options/SARs to acquire shares of Company common stock were excluded from the computations of diluted earnings per share for the three months ended March 31, 2021.