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, 2023	Mar. 31, 2022
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 16,142	$ 44,809
Weighted-average number of common shares outstanding		22,757	22,896
Basic earnings per share		$ 0.71	$ 1.96
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 16,142	$ 44,809
Weighted-average number of common shares outstanding		22,757	22,896
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		1
Weighted-average shares applicable to diluted earnings		22,994	23,167
Diluted earnings per share		$ 0.70	$ 1.93
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	99
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]	108	120
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)		29	52

[1] 403,711 and 364,350 options/SARs to acquire shares of the Company's common stock were excluded from the computation of dilutive earnings per share for the three months ended March 31, 2023 and 2022, respectively. The options/SARs' exercise prices were greater than the average market price for the Company's common stock and inclusion of the instruments would have had an antidilutive effect on the computations of the earnings per share.