Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Mar. 31, 2015	Mar. 31, 2014
CPG MGP
Commitments and Contingencies
Environmental remediation expense	$ 1,800
PNG MGP
Commitments and Contingencies
Environmental remediation expense	1,100
CPG and PNG COAs
Commitments and Contingencies
Option to termination agreement by either party effective at end of any two-year period beginning with the original effective date in March 2004 (in years)	2 years
Accrual for environmental loss contingencies	$ 9,610	$ 11,097
Environmental Issue
Commitments and Contingencies
Base year for determination of investigation and remediation cost (in years)	5 years

Base year for determination of investigation and remediation cost.

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Option to Termination Agreement By Either Party Effective at End of Any Period

+ References

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

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-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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-Name Accounting Standards Codification

-Topic 410

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-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13296-110859

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