Earnings Per Share - Computations 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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 23,606	$ 12,571	$ 47,020	$ 41,397
Weighted-average number of common shares outstanding		22,836	22,786	22,829	22,770
Basic earnings per share		$ 1.03	$ 0.55	$ 2.06	$ 1.82
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 23,606	$ 12,571	$ 47,020	$ 41,397
Weighted-average number of common shares outstanding		22,836	22,786	22,829	22,770
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		9	3	7	2
Weighted-average shares applicable to diluted earnings		22,923	22,930	22,936	22,956
Diluted earnings per share		$ 1.03	$ 0.55	$ 2.05	$ 1.8
Stock Option [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)	[1]	25	54	36	75
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]	28	53	42	78
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)		25	34	22	31

[1] 883,188 and 860,788 options/SARs to acquire shares of the Company's common stock were excluded from the computation of dilutive earnings per share for the three and nine months ended September 30, 2024, 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. 822,271 and 623,648 options/SARs to acquire shares of the Company's common stock were excluded from the computation of dilutive earnings per share for the three and nine months ended September 30, 2023, respectively.