Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Computation of Basic Earnings per Share
Net income attributable to Stepan Company	$ 20,230	$ 19,169	$ 63,957	$ 58,797
Deduct dividends on preferred stock	178	178	533	536
Income applicable to common stock	20,052	18,991	63,424	58,261
Weighted-average number of shares outstanding	10,581	10,365	10,553	10,345
Basic earnings per share	$ 1.90	$ 1.83	$ 6.01	$ 5.63
Computation of Diluted Earnings per Share
Net income attributable to Stepan Company	$ 20,230	$ 19,169	$ 63,424	$ 58,797
Weighted-average number of shares outstanding	10,581	10,365	10,553	10,345
Add weighted-average net shares issuable from assumed exercise of options (under treasury stock method)	193	237	207	241
Add weighted-average contingently issuable net shares related to performance stock awards (under treasury stock method)		51		17
Add weighted-average net shares related to unvested stock awards (under treasury stock method)	3	2	3	2
Add weighted-average shares issuable from assumed conversion of convertible preferred stock	591	593	591	594
Weighted-average shares applicable to diluted earnings	11,368	11,248	11,354	11,199
Diluted earnings per share	$ 1.78	$ 1.70	$ 5.63	$ 5.25