Reconciliations of Equity - Reconciliations of Total Equity (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reconciliations of total equity
Beginning Balance				$ 635,916	$ 558,384
Net income	[1]	$ 27,896	$ 28,501	59,808	56,420
Dividends				(9,225)	(8,477)
Common stock purchases	[2]			(3,191)	(2,643)
Stock option exercises				2,518	1,351
Defined benefit pension adjustments, net of tax		567	565	1,132	1,129
Translation adjustments		5,997	(2,692)	16,451	9,898
Derivative instrument activity, net of tax		(3)	(6)	(5)	(27)
Other	[3]			5,295	4,224	[4]
Ending Balance		708,699	620,259	708,699	620,259
Stepan Company Equity [Member]
Reconciliations of total equity
Beginning Balance				634,604	556,984
Net income				59,795	56,412
Dividends				(9,225)	(8,477)
Common stock purchases	[2]			(3,191)	(2,643)
Stock option exercises				2,518	1,351
Defined benefit pension adjustments, net of tax				1,132	1,129
Translation adjustments				16,418	9,931
Derivative instrument activity, net of tax				(5)	(27)
Other	[3]			5,295	4,224	[4]
Ending Balance		707,341	618,884	707,341	618,884
Noncontrolling Interests' Equity [Member]
Reconciliations of total equity
Beginning Balance	[5]			1,312	1,400
Net income	[5]			13	8
Translation adjustments	[5]			33	(33)
Ending Balance	[5]	$ 1,358	$ 1,375	$ 1,358	$ 1,375

[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 Company shares purchased in the open market and the value of Company common shares tendered by employees to settle statutory withholding taxes related to the receipt of performance awards and deferred compensation distributions.

[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.