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, 2024	Dec. 31, 2023	Dec. 31, 2022
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 50,370	$ 40,204	$ 147,153
Weighted-average number of shares outstanding		22,832	22,777	22,781
Basic earnings per share		$ 2.21	$ 1.77	$ 6.46
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 50,370	$ 40,204	$ 147,153
Weighted-average number of shares outstanding		22,832	22,777	22,781
Add weighted-average net shares related to unvested stock awards (under treasury share method)		6	3	1
Weighted-average shares applicable to diluted earnings		22,931	22,946	23,064
Diluted earnings per share		$ 2.2	$ 1.75	$ 6.38
Stock Option [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)	[1]	32	66	104
Stock Appreciation Rights (SARs)
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)		37	67	111
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)		24	33	67

[1] Options/SARs to purchase 888,726, 672,485 and 343,715 shares of the Company’s common stock were excluded from the computations of diluted earnings per share for the years ended December 31, 2024, 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 earnings per share.