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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Computation of Basic Earnings per Share
Net income attributable to Stepan Company		$ 39,384	$ 36,920	$ 136,319	$ 120,809
Weighted-average number of common shares outstanding		22,753	22,898	22,813	22,941
Basic earnings per share		$ 1.73	$ 1.61	$ 5.98	$ 5.27
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company		$ 39,384	$ 36,920	$ 136,319	$ 120,809
Weighted-average number of common shares outstanding		22,753	22,898	22,813	22,941
Add weighted-average net shares from assumed exercise of options (under treasury stock method)	[1]			111
Add weighted-average net shares related to unvested stock awards (under treasury stock method)		2		1	1
Weighted-average shares applicable to diluted earnings		23,034	23,219	23,089	23,299
Diluted earnings per share		$ 1.71	$ 1.59	$ 5.90	$ 5.19
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	124	105	139
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	142		168
Performance Stock Award [Member]
Computation of Diluted Earnings per Share
Add weighted-average net shares from assumed exercise of options (under treasury stock method)		69	55	59	50

[1] 336,727 and 346,044 options/SARs to acquire shares of Company common stock were excluded from the computation of dilutive earnings per share for the three and nine months ended September 30, 2022, respectively. 207,598 and 69,199 options/SARs to acquire shares of Company common stock were excluded from the computations of diluted earnings per share for the three and nine months ended September 30, 2021, respectively. Inclusion of the instruments would have had an antidilutive effect on the computations of the earnings per share.