Summary of Significant Accounting Policies - Additional Information (Detail) MMBTU in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) MMBTU Customer Subsidiary	Dec. 31, 2016 USD ($) Customer	Dec. 31, 2015 USD ($) Customer	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policy [Line Items]
Cash and cash equivalents	$ 298,894,000	$ 225,743,000	$ 176,143,000	$ 85,215,000
Single customer comprised more than 10 percent of the Company's consolidated net sales | Customer	0	0	0
Percentage of LIFO Inventory	69.00%	66.00%
Cost of maintenance and repairs	$ 51,926,000	$ 51,530,000	$ 52,549,000
Total research and development expenses	$ 33,169,000	$ 34,856,000	$ 30,315,000
Capitalized Environmental expenditures depreciation period	10 years
Indefinite-life intangible assets	$ 0
Number of foreign subsidiaries | Subsidiary	2
Natural Gas [Member]
Summary Of Significant Accounting Policy [Line Items]
Volume in derivative contract | MMBTU	0.8
Purchased Contract Price	$ 2,521,000
Non-compete Agreements [Member]
Summary Of Significant Accounting Policy [Line Items]
Finite-lived intangible asset, useful life	5 years
Trademarks [Member]
Summary Of Significant Accounting Policy [Line Items]
Finite-lived intangible asset, useful life	11 years
Supply contracts [Member]
Summary Of Significant Accounting Policy [Line Items]
Finite-lived intangible asset, useful life	4 years
Know-how [Member]
Summary Of Significant Accounting Policy [Line Items]
Finite-lived intangible asset, useful life	8 years
Building [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	30 years
Building Improvements [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	15 years
Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Percentage of Tax benefit recognized	50.00%
Minimum [Member] | Patents [Member]
Summary Of Significant Accounting Policy [Line Items]
Finite-lived intangible asset, useful life	10 years
Minimum [Member] | Customer Relationships [Member]
Summary Of Significant Accounting Policy [Line Items]
Finite-lived intangible asset, useful life	10 years
Minimum [Member] | Manufacturing Equipment [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	10 years
Minimum [Member] | Furniture and Fixtures [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	5 years
Minimum [Member] | Vehicles [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	3 years
Minimum [Member] | Computers Equipment And Software [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	3 years
Maximum [Member] | Patents [Member]
Summary Of Significant Accounting Policy [Line Items]
Finite-lived intangible asset, useful life	15 years
Maximum [Member] | Customer Relationships [Member]
Summary Of Significant Accounting Policy [Line Items]
Finite-lived intangible asset, useful life	13 years
Maximum [Member] | Manufacturing Equipment [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	15 years
Maximum [Member] | Furniture and Fixtures [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	10 years
Maximum [Member] | Vehicles [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	5 years
Maximum [Member] | Computers Equipment And Software [Member]
Summary Of Significant Accounting Policy [Line Items]
Lives used for calculating depreciation expense	10 years
Money Market Funds [Member]
Summary Of Significant Accounting Policy [Line Items]
Cash and cash equivalents	$ 15,100,000
Demand Deposits [Member]
Summary Of Significant Accounting Policy [Line Items]
Cash and cash equivalents	131,900,000
Non-U.S. Subsidiaries [Member]
Summary Of Significant Accounting Policy [Line Items]
Cash and cash equivalents	$ 151,900,000
Nanjing Stepan Jinling Chemical Limited Liability Company [Member]
Summary Of Significant Accounting Policy [Line Items]
Ownership percentage	80.00%