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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - RECEIVABLE BY SUBSIDIARY (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Establishment of allowance for doubtful accounts, customer account balances, days outstanding (more than)	60 days
Billed	$ 196,467	$ 142,658
Receivable by subsidiary percentage	100.00%	100.00%
Unbilled revenues	$ 7,202	$ 5,744
Energy Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	$ 150,322	$ 102,884
Receivable by subsidiary percentage	77.00%	72.00%
Natural Gas Distribution
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	$ 37,432	$ 30,951
Receivable by subsidiary percentage	19.00%	22.00%
Clean Energy Ventures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	$ 2,655	$ 1,807
Receivable by subsidiary percentage	1.00%	1.00%
NJRHS and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Billed	$ 6,058	$ 7,016
Receivable by subsidiary percentage	3.00%	5.00%

X

- Definition

Establishment of Allowance for Doubtful Accounts, Days Outstanding

+ References

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- Definition

Receivable by Subsidiary Percentage

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- Definition

Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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(5))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Amount received for services rendered and products shipped, but not yet billed, for non-contractual agreements due within one year or the normal operating cycle, if longer.

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