Related Party Transactions (Details) $ in Thousands	3 Months Ended
Dec. 31, 2016 USD ($) Bcf	Dec. 31, 2015 USD ($) Bcf	Sep. 30, 2016 USD ($) Bcf
Related Party Transaction
Related party costs incurred	$ 2,564	$ 2,180
Energy Services
Related Party Transaction
Revenue from related parties	$ 10,972	8,766
Term of agreements (in years)	1 year
Purchases from related party	$ 22,023	$ 8,192
Energy Services \| Inventory
Related Party Transaction
Volume of gas storage inventory (in bcf of natural gas) \| Bcf	5.9	5.1	4.6
Natural gas storage inventory, related parties, current	$ 12,851	$ 12,684	$ 11,148
Energy Services \| SCAAs
Related Party Transaction
SCAA contract term (in years)	3 years
Related party costs incurred	$ 2,294	1,870
Energy Services \| SCAAs \| Other Current Liabilities
Related Party Transaction
Related party security deposits	11,000	8,100	$ 8,100
Energy Services \| Exclusive of Transactions Pursuant SCAAs
Related Party Transaction
Related party costs incurred	$ 30,510	$ 27,364

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Related Parties
-URI http://asc.fasb.org/extlink&oid=16382449

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 225
-Section S99
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-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

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