Commitments and Contingencies - Narrative (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
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	$ 11,097	$ 14,338
Environmental Issue
Commitments and Contingencies
Base year for determination of investigation and remediation cost (in years)	5 years