Commitments and Contingencies (Legal Matters and New Mexico Audits) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012
Pending or threatened legal proceedings
Loss Contingencies [Line Items]
Accrued provision for estimated liability	$ 100,000
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Order for payment of additional royalties	142,000
Preliminary estimates of order maximum liabilities for additional royalties	$ 23,000,000
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.