Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Contingencies
Rental expense	$ 7,956	$ 6,803	$ 6,270
Base year for determination of investigation and remediation cost	5 years
Minimum future payments under operating leases
2016	$ 6,438
2017	4,818
2018	3,869
2019	1,621
2020	591
After 2020	448
Contractual obligations under suplly, storage and service agreements
2016	204,881
2017	118,795
2018	87,254
2019	74,621
2020	56,983
After 2020	$ 93,596
Gas Utility
Contingencies
Duration of supply agreements - not more than (in months)	16 months
CPG-COA and PNG-COA
Contingencies
Accrued liabilities for environmental investigation and remediation costs	$ 13,758	$ 10,732
CPG MGP
Contingencies
Environmental expenditures cap during year	1,800
PNG MGP
Contingencies
Environmental expenditures cap during year	$ 1,100
Option to termination agreement by either party effective at end of any two-year period	2 years