Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net Sales		$ 507,997	$ 487,814		$ 1,527,198	$ 1,451,184
Cost of Sales	[1]	423,872	412,238		1,264,223	1,193,501
Gross Profit	[1]	84,125	75,576		262,975	257,683
Operating Expenses:
Selling	[1]	14,613	13,710		42,872	40,396
Administrative	[1]	21,904	18,480		59,441	54,141
Research, development and technical services	[1]	13,977	12,655		41,311	40,288
Deferred compensation expense		4,222	(129)		4,971	5,263
Total Operating expenses		54,716	44,716		148,595	140,088
Business restructuring expenses (Note 15)		(1,715)	(426)	[2]	(2,346)	(1,798)	[2]
Operating Income	[1]	27,694	30,434	[2]	112,034	115,797	[2]
Other Income (Expense):
Interest, net		(2,797)	(2,763)	[2]	(8,620)	(8,618)	[2]
Other, net (Note 14)	[1]	346	1,641	[2]	1,990	3,526	[2]
Nonoperating Income (Expense), Total		(2,451)	(1,122)		(6,630)	(5,092)
Income Before Provision for Income Taxes		25,243	29,312	[2]	105,404	110,705	[2]
Provision for Income Taxes (Note 17)		3,075	7,459		19,597	29,044
Net Income		22,168	21,853		85,807	81,661
Net Loss Attributable to Noncontrolling Interests (Note 2)			46		9	33
Net Income Attributable to Stepan Company		$ 22,168	$ 21,899		$ 85,816	$ 81,694
Net Income Per Common Share Attributable to Stepan Company (Note 9):
Basic		$ 0.96	$ 0.95		$ 3.73	$ 3.56
Diluted		$ 0.95	$ 0.94		$ 3.68	$ 3.50
Shares Used to Compute Net Income Per Common Share Attributable to Stepan Company (Note 9):
Basic		22,986	22,971		23,036	22,941
Diluted		23,288	23,374		23,324	23,361
Dividends Declared Per Common Share		$ 0.23	$ 0.21		$ 0.68	$ 0.62

[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