Revenue Recognition - Additional Information (Detail) - USD ($)	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Revenue Recognition [Line Items]
Revenue, practical expedient, incremental cost of obtaining contract [true false]	true
Contract costs, amortization period	5 years
Contract costs, impairment loss	$ 0
Contract liabilities	139,600,000	$ 127,000,000.0
Contract with customer liability, revenue recognized	118,600,000	111,000,000.0
Prepaid Expense and Other Current Assets
Revenue Recognition [Line Items]
Deferred contract costs,current	3,400,000	3,400,000
Deferred Charges and Other Assets, Net
Revenue Recognition [Line Items]
Deferred contract costs,non current	5,900,000	5,900,000
Delivery and Branch Expenses
Revenue Recognition [Line Items]
Amortization of deferred contract costs	$ 4,000,000.0	$ 4,000,000.0
Maximum
Revenue Recognition [Line Items]
Contract liabilities recognition service contract period	1 year
Equipment Maintenance Service Contracts \| Maximum
Revenue Recognition [Line Items]
Revenue from service contracts period of recognition	1 year
Residential and Commercial Home Heating Oil Customers
Revenue Recognition [Line Items]
Percentage of customers receiving deliveries based on prevailing weather conditions	95.00%
Residential Customers
Revenue Recognition [Line Items]
Customer payment terms	30 days
Percentage of customers take advantage of smart pay budget payment plan	34.00%

Contract liabilities recognition service contract period.

No definition available.

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- Definition

Customer payment terms.

+ References

No definition available.

+ Details

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- Definition

Percentage of customers receiving deliveries based on prevailing weather conditions.

+ References

No definition available.

+ Details

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- Definition

Percentage of customers take advantage of smart pay budget payment plan.

+ References

No definition available.

+ Details

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- Definition

Revenue from service contracts period of recognition.

+ References

No definition available.

+ Details

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- Definition

Revenue recognition.

+ References

No definition available.

+ Details

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- Definition

Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

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- Definition

Amortization period of cost capitalized in obtaining or fulfilling contract with customer, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131251-203054

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- Definition

Amount of impairment loss for asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

+ Details

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- Definition

Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer; classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

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- Definition

Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer; classified as noncurrent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

+ Details

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- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130532-203044

+ Details

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- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045

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- Definition

Indicates (true false) whether practical expedient was elected to recognize incremental cost of obtaining contract as expense when incurred if amortization period would have been one year or less.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL51790836-203054

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130569-203045

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