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Acquisitions - Additional Information (Detail)						3 Months Ended
Acquisitions - Additional Information (Detail)	Mar. 31, 2021 USD ($)	Feb. 02, 2021 USD ($)	Jan. 29, 2021 USD ($) Site	Sep. 17, 2020 USD ($)	Mar. 13, 2020 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)
Business Acquisition [Line Items]
Purchase price						$ 184,000,000
Payment of working capital			$ 21,000,000
Payment of value added tax			3,000,000
Cash acquired on working capital			$ 5,000,000
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							$ 1,285,000
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						1,285,000
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						3,232,000
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			$ 24,500,000
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	$ 13,519,000
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