Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net Sales		$ 519,866	$ 495,101		$ 1,019,201	$ 963,370
Cost of Sales	[1]	430,586	405,113		840,351	781,263
Gross Profit	[1]	89,280	89,988		178,850	182,107
Operating Expenses:
Selling	[1]	13,369	13,230		28,259	26,686
Administrative	[1]	18,098	17,769		37,537	35,661
Research, development and technical services	[1]	13,720	14,254		27,334	27,633
Deferred compensation expense		(865)	5,016		749	5,392
Total Operating expenses		44,322	50,269		93,879	95,372
Business restructuring expenses (Note 15)		(273)	(586)	[2]	(631)	(1,372)	[2]
Operating Income	[1]	44,685	39,133	[2]	84,340	85,363	[2]
Other Income (Expense):
Interest, net		(2,672)	(2,863)	[2]	(5,823)	(5,855)	[2]
Other, net (Note 14)	[1]	484	793	[2]	1,644	1,885	[2]
Nonoperating Income (Expense), Total		(2,188)	(2,070)		(4,179)	(3,970)
Income Before Provision for Income Taxes		42,497	37,063	[2]	80,161	81,393	[2]
Provision for Income Taxes (Note 17)		9,574	9,167		16,522	21,585
Net Income		32,923	27,896		63,639	59,808
Net (Income) Loss Attributable to Noncontrolling Interests (Note 2)		2	(14)		9	(13)
Net Income Attributable to Stepan Company		$ 32,925	$ 27,882		$ 63,648	$ 59,795
Net Income Per Common Share Attributable to Stepan Company (Note 9):
Basic		$ 1.43	$ 1.21		$ 2.76	$ 2.61
Diluted		$ 1.41	$ 1.19		$ 2.73	$ 2.56
Shares Used to Compute Net Income Per Common Share Attributable to Stepan Company (Note 9):
Basic		23,039	22,953		23,059	22,927
Diluted		23,295	23,381		23,341	23,356
Dividends Declared Per Common Share		$ 0.23	$ 0.21		$ 0.45	$ 0.41

[1] The 2017 amounts for the noted line items have been immaterially changed from the amounts originally reported as a result of the Company’s first quarter 2018 adoption of Accounting Standards Update (ASU) No. 2017-7, Compensation –Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.

[2] The 2017 data has been immaterially changed from the amounts originally reported as a result of the Company’s first quarter 2018 adoption of ASU No. 2017-7, Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.