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Acquisitions - Additional Information (Detail)					3 Months Ended	9 Months Ended
Acquisitions - Additional Information (Detail)	Feb. 02, 2021 USD ($)	Jan. 29, 2021 USD ($) Site	Sep. 17, 2020 USD ($)	Mar. 13, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Business Acquisition [Line Items]
Payment of working capital		$ 21,560,000
Payment of value added tax		3,000,000
Cash acquired on working capital		$ 5,900,000
Purchase price						$ 3,503,000	$ 2,040,000
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| 2021 Acquisitions [Member] \| Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Net income attributable to Stepan Company						2,078,000
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member]
Business Acquisition [Line Items]
Asset purchase agreement date		Jan. 29, 2021
Number of manufacturing site \| Site		2
Purchase price		$ 165,000,000
Acquisition-related expenses					$ 474,000	2,078,000
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member] \| Legal, Consulting, Valuation and Accounting Services [Member]
Business Acquisition [Line Items]
Acquisition-related expenses						4,025,000
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member] \| Technology and Manufacturing Know-how [Member]
Business Acquisition [Line Items]
Identifiable intangible assets		13,000,000
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member] \| Trademarks [Member]
Business Acquisition [Line Items]
Identifiable intangible assets		8,000,000
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member] \| Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets		$ 25,000,000
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member] \| Customer Relationships [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Weighted average amortization periods of identifiable intangibles assets		12 years
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member] \| Customer Relationships [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Weighted average amortization periods of identifiable intangibles assets		14 years
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member] \| Know-how and Trademarks [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Weighted average amortization periods of identifiable intangibles assets		7 years
INVISTA Aromatic Polyester Polyol Business Acquisition [Member] \| Polymers [Member] \| 2021 Acquisitions [Member] \| Know-how and Trademarks [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Weighted average amortization periods of identifiable intangibles assets		8 years
Fermentation Plant Acquisition [Member] \| 2021 Acquisitions [Member]
Business Acquisition [Line Items]
Purchase price	$ 3,500,000
Clariant (Mexico) [Member] \| Surfactants [Member] \| 2020 Acquisitions [Member]
Business Acquisition [Line Items]
Purchase price						14,308,000
Payment of value added tax					$ 308,000	$ 308,000
Purchase price			$ 14,000,000
Clariant (Mexico) [Member] \| Surfactants [Member] \| 2020 Acquisitions [Member] \| Trademarks and Know-how [Member]
Business Acquisition [Line Items]
Identifiable intangible assets			$ 1,300,000
Logos Technologies Asset Acquisition [Member] \| Surfactants [Member] \| 2020 Acquisitions [Member]
Business Acquisition [Line Items]
Purchase price				$ 2,040,000
Logos Technologies Asset Acquisition [Member] \| Surfactants [Member] \| 2020 Acquisitions [Member] \| Laboratory Equipment [Member]
Business Acquisition [Line Items]
Equipment acquired				184,000
Logos Technologies Asset Acquisition [Member] \| Surfactants [Member] \| 2020 Acquisitions [Member] \| Trademarks and Know-how [Member]
Business Acquisition [Line Items]
Intangible assets acquired				1,392,000
Logos Technologies Asset Acquisition [Member] \| Surfactants [Member] \| 2020 Acquisitions [Member] \| Patents [Member]
Business Acquisition [Line Items]
Intangible assets acquired				$ 464,000