Fair Value Measurements (Narrative) (Details) - USD ($)		12 Months Ended
		Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits	[1]	$ 11,124,000	$ 2,734,000
Assumed 12 month Midway Sunset Oil comparison to NYMEX		91.80%
Assumed 12 month minimum Midway Sunset Oil comparison to NYMEX		87.80%
Assumed 12 month maximum Midway Sunset Oil comparison to NYMEX		94.60%
Fair value measured on recurring basis, net	[1]	$ 411,263,000	140,790,000
Level 1 or Level 2 Transfers		0	0
Derivative Financial Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Level 1 or Level 2 Transfers		0	0
Sales of Derivative Financial Instruments		0	0
Purchases of Derivative Financial Instruments		0	0
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits		11,124,000	2,734,000
Fair value measured on recurring basis, net		142,073,000	68,994,000
Fair Value, Inputs, Level 1 [Member] | Futures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Hedging collateral deposits		11,100,000	2,700,000
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		$ 1,791,000	$ 1,368,000
Lower [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Midway Sunset Oil Comparison to NYMEX Sensitivity percentage points		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		$ 200,000
Higher [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Midway Sunset Oil Comparison to NYMEX Sensitivity percentage points		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		$ (200,000)

[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.