Consolidated Statements of Income - USD ($) shares in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net Sales (Note 1)	[1]	$ 1,925,007,000	$ 1,766,166,000	$ 1,776,167,000
Cost of Sales		1,586,742,000	1,427,621,000	1,467,926,000
Gross Profit		338,265,000	338,545,000	308,241,000
Operating Expenses:
Selling (Note 1)		54,271,000	57,212,000	55,522,000
Administrative (Note 1)		76,041,000	75,185,000	76,048,000
Research, development and technical services (Note 1)		53,867,000	56,086,000	50,243,000
Deferred compensation expense		4,857,000	16,805,000	6,500,000
Total Operating expenses		189,036,000	205,288,000	188,313,000
Gain on sale of product line				2,862,000
Business restructuring and asset impairments (Note 22)		(3,069,000)	(7,064,000)
Operating Income		146,160,000	126,193,000	122,790,000
Other Income (Expense):
Interest, net (Note 6)		(11,444,000)	(13,205,000)	(14,533,000)
Loss from equity in joint ventures (Notes 1 and 25)				(6,985,000)
Other, net (Note 8)		4,521,000	828,000	1,584,000
Nonoperating Income (Expense), Total		(6,923,000)	(12,377,000)	(19,934,000)
Income Before Provision for Income Taxes		139,237,000	113,816,000	102,856,000
Provision for Income Taxes (Note 9)		47,690,000	27,618,000	26,819,000
Net Income		91,547,000	86,198,000	76,037,000
Net (Income) Loss Attributable to Noncontrolling Interests (Note 1)		31,000	(7,000)	(69,000)
Net Income Attributable to Stepan Company		$ 91,578,000	$ 86,191,000	$ 75,968,000
Net Income Per Common Share Attributable to Stepan Company (Note 18):
Basic		$ 3.99	$ 3.78	$ 3.34
Diluted		$ 3.92	$ 3.73	$ 3.32
Shares Used to Compute Net Income Per Common Share Attributable to Stepan Company (Note 18):
Basic		22,946	22,793	22,730
Diluted		23,377	23,094	22,858

[1] Net sales are attributed to countries based on the location of the Company facility making the sales.