Fair Value Measurements (Narrative) (Details) (USD $)	6 Months Ended
	Mar. 31, 2013	Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits	$ 750,000	$ 364,000
Assumed 12 month basis differential comparison to NYMEX	110.50%
Assumed 12 month minimum basis differential comparison to NYMEX	108.50%
Assumed 12 month maximum basis differential comparison to NYMEX	112.40%
Fair Value Measured On Recurring Basis, Net	89,772,000	79,363,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits	750,000	364,000
Fair Value Measured On Recurring Basis, Net	126,346,000	77,862,000
Fair Value, Inputs, Level 1 [Member] | NYMEX Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits		400,000
Fair Value, Inputs, Level 1 [Member] | Over-The-Counter Swap Position [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits	800,000
Higher [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Basis Differential On NYMEX Sensitivity	10.00%
Fair value of crude oil price swap sensitivity	(13,100,000)
Lower [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Basis Differential On NYMEX Sensitivity	10.00%
Fair value of crude oil price swap sensitivity	$ 13,100,000