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Summary of Significant Accounting Policies - Summary of Estimated Useful Life of Fixed Assets (Detail)	12 Months Ended
	Dec. 31, 2017
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives, years	Shorter of the lease term or useful life of the asset
Refined Fuel Plants [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	10 years
Minimum [Member] | Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	3 years
Minimum [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	3 years
Minimum [Member] | Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	3 years
Minimum [Member] | Software [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	3 years
Minimum [Member] | Building [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	15 years
Maximum [Member] | Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	5 years
Maximum [Member] | Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	10 years
Maximum [Member] | Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	10 years
Maximum [Member] | Software [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	5 years
Maximum [Member] | Building [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	40 years

X

- Definition

Describes the periods of time over which an entity anticipates to receive utility from its property, plant and equipment (that is, the periods of time over which an entity allocates the initial cost of its property, plant and equipment).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 35
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68071081&loc=d3e1205-110223

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

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