Fair Value Measurements (Narrative) (Details) (USD $)	6 Months Ended
	Mar. 31, 2014		Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits	$ 0	[1]	$ 1,094,000	[1]
Assumed 12 month basis differential comparison to NYMEX	100.30%
Assumed 12 month minimum basis differential comparison to NYMEX	96.20%
Assumed 12 month maximum basis differential comparison to NYMEX	108.10%
Fair value measured on recurring basis, net	175,854,000	[1]	139,452,000	[1]
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits	0		1,094,000
Fair value measured on recurring basis, net	174,763,000		92,024,000
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			1,100,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits	0		0
Fair value measured on recurring basis, net	(1,371,000)		(5,190,000)
Fair Value, Inputs, Level 3 [Member] | Over The Counter Swaps - Oil [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measured on recurring basis, net	1,400,000
Higher [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Basis Differential On NYMEX Sensitivity	10.00%
Higher [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of crude oil price swap sensitivity	5,800,000
Lower [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Basis Differential On NYMEX Sensitivity	10.00%
Lower [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of crude oil price swap sensitivity	$ 4,400,000

[1] Netting Adjustments represent the impact of legally-enforceable master netting arrangements that allow the Company to net gain and loss positions held with the same counterparties. The net asset or net liability for each counterparty is recorded as an asset or liability on the Company’s balance sheet.