Earnings Per Share - Computations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 52,126	$ 43,278	$ 96,935	$ 83,889
Weighted-average number of common shares outstanding		22,792	22,952	22,842	22,963
Basic earnings per share		$ 2.29	$ 1.89	$ 4.24	$ 3.65
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 52,126	$ 43,278	$ 96,935	$ 83,889
Weighted-average number of common shares outstanding		22,792	22,952	22,842	22,963
Add weighted-average net shares related to unvested stock awards (under treasury stock method)			1		1
Weighted-average shares applicable to diluted earnings		23,055	23,345	23,115	23,338
Diluted earnings per share		$ 2.26	$ 1.85	$ 4.19	$ 3.59
Stock Option [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)	[1]	102	152	106	146
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]	106	190	113	181
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)		55	50	54	47

[1] 337,056 and 350,703 options/SARs to acquire shares of Company common stock were excluded from the computation of dilutive earnings per share for the three and six months ended June 30, 2022, respectively. 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 and six months ended June 30, 2021.