Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018		Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Net Sales		$ 473,003	$ 519,866		$ 962,173	$ 1,019,201
Cost of Sales	[1]	380,044	429,885		784,605	838,022
Gross Profit	[1]	92,959	89,981		177,568	181,179
Operating Expenses:
Selling		14,140	13,369		28,109	28,259
Administrative		21,544	18,098		40,850	37,537
Research, development and technical services		13,365	13,720		26,755	27,334
Deferred compensation expense (income)		2,395	(865)		9,868	749
Total Operating expenses		51,444	44,322		105,582	93,879
Business restructuring expenses (Note 17)		(450)	(273)		(1,183)	(631)
Operating Income	[1],[2]	41,065	45,386		70,803	86,669
Other Income (Expense):
Interest, net		(1,766)	(2,672)		(3,619)	(5,823)
Other, net (Note 16)		235	484		3,380	1,644
Nonoperating Income (Expense), Total		(1,531)	(2,188)		(239)	(4,179)
Income Before Provision for Income Taxes	[1],[2]	39,534	43,198		70,564	82,490
Provision for Income Taxes	[1]	9,324	9,746		15,376	17,093
Net Income	[1],[2]	30,210	33,452	[3]	55,188	65,397
Net Loss Attributable to Noncontrolling Interests (Note 3)		8	2		14	9
Net Income Attributable to Stepan Company	[1],[2]	$ 30,218	$ 33,454		$ 55,202	$ 65,406
Net Income Per Common Share Attributable to Stepan Company (Note 11):
Basic	[1],[2]	$ 1.31	$ 1.45		$ 2.39	$ 2.84
Diluted	[1],[2]	$ 1.30	$ 1.44		$ 2.37	$ 2.80
Shares Used to Compute Net Income Per Common Share Attributable to Stepan Company (Note 11):
Basic		23,086	23,039		23,092	23,059
Diluted		23,329	23,295		23,329	23,341

[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.