Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities Including Offsetting Amounts (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Fair value of derivative assets, gross	$ 1,697	$ 92
Gross amounts offset in the balance sheet	(669)	(49)
Total derivative assets - net	1,028	43
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Fair value of derivative liabilities, gross	(2,301)	(6,726)
Gross amounts offset in the balance sheet	669	49
Total derivative liabilities - net	(1,632)	(6,677)
Commodity Contracts | Accounted for Under ASC 980 | Derivative Instruments, Assets
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Fair value of derivative assets, gross	1,697	80
Commodity Contracts | Accounted for Under ASC 980 | Derivative Instruments, Liabilities
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Fair value of derivative liabilities, gross	(2,210)	(6,726)
Commodity Contracts | Derivatives Not Designated as Hedging Instruments | Derivative Instruments, Assets
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Fair value of derivative assets, gross	0	12
Commodity Contracts | Derivatives Not Designated as Hedging Instruments | Derivative Instruments, Liabilities
Derivative Liability, Fair Value, Amount Not Offset Against Collateral [Abstract]
Fair value of derivative liabilities, gross	$ (91)	$ 0