Commitments and Contingencies - New Mexico Audits (Details) (USD $)	6 Months Ended
	Jun. 30, 2013
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Minimum loss contingency range of loss	$ 142,000
Maximum loss contingency range of possible loss	$ 23,000,000
Inestimable loss	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 March 31, 2013.
New Mexico
Loss Contingencies [Line Items]
Number of counties ONRR has ordered to restructure accounting on federal leases	2