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, 2025	Dec. 31, 2024	Dec. 31, 2023
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 46,895	$ 50,370	$ 40,204
Weighted-average number of shares outstanding		22,872	22,832	22,777
Basic earnings per share		$ 2.05	$ 2.21	$ 1.77
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 46,895	$ 50,370	$ 40,204
Weighted-average number of shares outstanding		22,872	22,832	22,777
Add weighted-average net shares related to unvested stock awards (under treasury share method)		5	6	3
Weighted-average shares applicable to diluted earnings		22,890	22,931	22,946
Diluted earnings per share		$ 2.05	$ 2.2	$ 1.75
Stock Option [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)	[1]	7	32	66
Stock Appreciation Rights (SARs)
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)		5	37	67
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury share method)		1	24	33

[1] Options/SARs to purchase 1,208,928, 888,726 and 672,485 shares of the Company’s common stock were excluded from the computations of diluted earnings per share for the years ended December 31, 2025, 2024 and 2023, 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.