Reconciliations of Equity - Reconciliations of Total Equity (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Reconciliations of total equity
Beginning Balance		$ 635,916	$ 558,384
Net income	[1]	31,912	27,919	[2]
Dividends		(4,606)	(4,237)
Common stock purchases	[3]	(2,991)	(1,143)
Stock option exercises		835	258
Defined benefit pension adjustments, net of tax		565	564
Translation adjustments		10,454	12,590
Derivative instrument activity, net of tax		(2)	(21)
Other	[4]	2,474	1,929	[2]
Ending Balance		674,557	596,243
Stepan Company Equity [Member]
Reconciliations of total equity
Beginning Balance		634,604	556,984
Net income		31,913	27,916	[2]
Dividends		(4,606)	(4,237)
Common stock purchases	[3]	(2,991)	(1,143)
Stock option exercises		835	258
Defined benefit pension adjustments, net of tax		565	564
Translation adjustments		10,441	12,579
Derivative instrument activity, net of tax		(2)	(21)
Other	[4]	2,474	1,929	[2]
Ending Balance		673,233	594,829
Noncontrolling Interests' Equity [Member]
Reconciliations of total equity
Beginning Balance	[5]	1,312	1,400
Net income	[5]	(1)	3	[2]
Translation adjustments	[5]	13	11
Ending Balance	[5]	$ 1,324	$ 1,414

[1] The 2016 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 Accounting Standards Update (ASU) No. 2019-9, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.

[2] 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.

[3] 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 distributions of deferred performance awards and deferred management incentive compensation and to exercises of stock appreciation rights.

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

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