Reconciliations of Equity - Reconciliations of Total Equity (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reconciliations of total equity
Beginning Balance				$ 635,916	$ 558,384
Net income	[1]	$ 21,853	$ 21,367	81,661	77,787
Dividends				(13,841)	(12,732)
Common stock purchases	[2]			(6,255)	(2,643)
Stock option exercises				3,127	3,290
Defined benefit pension adjustments, net of tax		539	497	1,671	1,626
Translation adjustments		9,837	(2,213)	26,288	7,685
Derivative instrument activity, net of tax		(2)		(7)	(27)
Other	[3]			7,711	6,362	[4]
Ending Balance		736,271	639,732	736,271	639,732
Stepan Company Equity [Member]
Reconciliations of total equity
Beginning Balance				634,604	556,984
Net income				81,694	77,774
Dividends				(13,841)	(12,732)
Common stock purchases	[2]			(6,255)	(2,643)
Stock option exercises				3,127	3,290
Defined benefit pension adjustments, net of tax				1,671	1,626
Translation adjustments				26,229	7,722
Derivative instrument activity, net of tax				(7)	(27)
Other	[3]			7,711	6,362	[4]
Ending Balance		734,933	638,356	734,933	638,356
Noncontrolling Interests' Equity [Member]
Reconciliations of total equity
Beginning Balance	[5]			1,312	1,400
Net income	[5]			(33)	13
Translation adjustments	[5]			59	(37)
Ending Balance	[5]	$ 1,338	$ 1,376	$ 1,338	$ 1,376

[1] The 2016 amounts for the noted items have been immaterially changed from the amounts originally reported as a result of the Company’s fourth quarter 2016 adoption of Accounting Standards Update (ASU) No. 2016-9, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.

[2] Includes the value of shares of the Company’s common stock purchased in the open market and tendered by employees to settle statutory withholding taxes related to the receipt of performance awards, the receipt of deferred compensation distributions and the exercises of stock appreciation rights (SARs).

[3] Primarily comprised of activity related to stock-based compensation and deferred compensation.

[4] Amounts for the noted line items have been immaterially changed from the amounts originally reported as a result of the Company’s fourth quarter 2016 adoption of ASU No. 2016-9, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.

[5] Reflects the noncontrolling interest in the Company’s China joint venture.