Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Net Sales		$ 451,582	$ 507,997		$ 1,413,755	$ 1,527,198
Cost of Sales	[1]	374,180	424,421		1,158,785	1,262,443
Gross Profit	[1]	77,402	83,576		254,970	264,755
Operating Expenses:
Selling		14,186	14,613		42,295	42,872
Administrative		19,708	21,904		60,558	59,441
Research, development and technical services		13,473	13,977		40,228	41,311
Deferred compensation expense		1,610	4,222		11,478	4,971
Total Operating expenses		48,977	54,716		154,559	148,595
Business restructuring expenses (Note 17)		(459)	(1,715)		(1,642)	(2,346)
Operating Income	[1],[2]	27,966	27,145		98,769	113,814
Other Income (Expense):
Interest, net		(1,402)	(2,797)		(5,021)	(8,620)
Other, net (Note 16)		885	346		4,265	1,990
Nonoperating Income (Expense), Total		(517)	(2,451)		(756)	(6,630)
Income Before Provision for Income Taxes	[1],[2]	27,449	24,694		98,013	107,184
Provision for Income Taxes	[1]	1,569	2,940		16,945	20,033
Net Income	[1],[2]	25,880	21,754	[3]	81,068	87,151	[3]
Net Loss Attributable to Noncontrolling Interests (Note 3)		9			23	9
Net Income Attributable to Stepan Company	[1],[2]	$ 25,889	$ 21,754		$ 81,091	$ 87,160
Net Income Per Common Share Attributable to Stepan Company (Note 11):
Basic	[1],[2]	$ 1.12	$ 0.95		$ 3.52	$ 3.78
Diluted	[1],[2]	$ 1.11	$ 0.93		$ 3.48	$ 3.74
Shares Used to Compute Net Income Per Common Share Attributable to Stepan Company (Note 11):
Basic		23,025	22,986		23,070	23,036
Diluted		23,300	23,288		23,320	23,324

[1] The 2018 amounts for the noted line items have been retrospectively changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from the last in, first out (LIFO) basis to the first in, first out (FIFO) basis.

[2] The 2018 amounts for the noted line items have been retrospectively changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from LIFO to FIFO.

[3] The retained earnings and net income amounts for the noted line items have been changed from the amounts originally reported as a result of the Company’s first quarter 2019 change in method of accounting for U.S. inventory valuation from LIFO to FIFO.