Selected Quarterly Financial Data (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	[1]	Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	[1]	Dec. 31, 2015	Dec. 31, 2014
Quarterly Data [Line Items]
Net Income	$ 8,411		$ 21,367	[1]	$ 28,501	[1]	$ 27,919	[1]	$ 12,876	$ 24,934	$ 16,941	$ 21,286	$ 86,198		$ 76,037	$ 57,081
Net income attributable to Stepan Company	$ 8,417		$ 21,362	[1]	$ 28,496	[1]	$ 27,916	[1]	$ 12,872	$ 24,912	$ 16,914	$ 21,270	$ 86,191		$ 75,968	$ 57,101
Diluted earnings per share	$ 0.36		$ 0.92	[1]	$ 1.24	[1]	$ 1.22	[1]	$ 0.56	$ 1.09	$ 0.74	$ 0.93	$ 3.73		$ 3.32	$ 2.49
New Accounting Pronouncement, Early Adoption [Member] | ASU No. 2016-9 [Member]
Quarterly Data [Line Items]
Net Income			$ 20,432		$ 27,870		$ 27,657
Net income attributable to Stepan Company			$ 20,427		$ 27,865		$ 27,654
Diluted earnings per share			$ 0.89		$ 1.21		$ 1.21

[1] The amounts for net income, net income attributable to Stepan Company and net income attributable to Stepan Company per diluted share for the first, second and third quarters of 2016 have been changed from the amounts originally reported as a result of the Company’s early adoption of ASU No. 2016-9, Compensation – Stock Compensation (Topic 718): Improvement to Employee Share-Based Payment Accounting. See Note 1 for additional information regarding ASU No. 2016-9. Below are the originally reported amounts for the items that changed: 2016 (In thousands, except per share data) First Second Third Net Income $27,657 $27,870 $20,432 Net Income Attributable to Stepan Company 27,654 27,865 20,427 Per Diluted Share 1.21 1.21 0.89