Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.1)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),2)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.

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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.

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- Definition

Nominal volume used to calculate payments on a derivative instrument.

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Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) gal in Millions, $ in Millions	6 Months Ended
	Mar. 31, 2017 USD ($) gal	Mar. 31, 2016 gal	Sep. 30, 2016 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Hedging positions secured under credit facility \| $	$ 3.3		$ 0.3
Prepaid expenses and other current assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregated cash posted as collateral in normal course of business \| $	$ 1.0
Call Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	2.1	3.4
Put Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	5.1	3.5
Synthetic calls \| Call Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	52.1	58.7
Inventory
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	8.0	5.4
Swap Contracts \| Long
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	0.3	0.7
Future Contracts \| Long
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	33.6	34.0
Future Contracts \| Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	47.6	53.1
Spread Contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	1.0	2.1
Hedge its Internal Fuel Usage and Other Related Activities Swap Contracts Bought
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	1.4	4.6