Financial Instruments - Summary of Outstanding Commodity Derivative Contracts (Details)	9 Months Ended
Sep. 30, 2020 $ / gal gal
Benzene Swaps
Derivative [Line Items]
Type	Benzene swaps
Unit of measure	U.S. liquid gallon
Contracted volume \| gal	199,827
Contracted date of maturity	2020-11
Benzene Swaps \| Minimum
Derivative [Line Items]
Contracted price range	1.25
Benzene Swaps \| Maximum
Derivative [Line Items]
Contracted price range	1.25
Diesel Swaps
Derivative [Line Items]
Type	Diesel swaps
Unit of measure	U.S. liquid gallon
Contracted volume \| gal	1,771,810
Contracted date of maturity, start	2020-10
Contracted date of maturity, end	2021-06
Diesel Swaps \| Minimum
Derivative [Line Items]
Contracted price range	2.30
Diesel Swaps \| Maximum
Derivative [Line Items]
Contracted price range	3.16

Description of the type of derivative instrument, such as a swap, forward, and option. Excludes the underlying risk of the instrument.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(n)(2))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579240-113959

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