Commitments and Contingencies (Legal Matters and New Mexico Audits) (Details) (USD $)	12 Months Ended	3 Months Ended
	Dec. 31, 2011 Pending or threatened legal proceedings	Sep. 30, 2011 Unfavorable Regulatory Action	Dec. 31, 2011 Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Accrued provision for estimated liability	$ 3,000,000
Order for payment of additional royalties			142,000
Preliminary estimates of order maximum liabilities for additional royalties			$ 21,000,000
Loss contingency, inestimable loss description		The preliminary findings and subsequent Order (issued April 25, 2011) are contrary to deductions allowed under previous audits, retroactive in application and inconsistent with the Company’s understanding of industry practice. The Company is vigorously contesting the Order and has requested additional information from the ONRR and the Department to assist the Company in evaluating the ONRR Order and the Department's findings. Management is unable, at this time, to determine a range of reasonably possible losses as a result of this Order, and no amount has been accrued as of December 31, 2011.