Acquisition and Development Agreement and Carry and Earning Agreement (Details) (USD $)			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Mitsui E&P Texas LP	Jun. 30, 2011 Mitsui E&P Texas LP
Acquisition and Development Agreement [Abstract]
Percentage of working interests transferred to acquiree entity (as a percent)				12.50%
Acreage of working interests transferred to acquiree entity (in acres)				39,000
Percentage of the entity's costs and expenses during the first three years following the closing of the transaction, borne by the acquiree entity (as a percent)			90.00%
Costs and expenses incurred by acquiree entity on behalf of entity that the acquiree entity has agreed to pay				$ 680,000,000
Portion of Drilling and Completion Costs Not Carried by Acquirer			10.00%
Restricted cash	96,713,000	86,773,000	94,959,000
Carry Amount, Portion Used to Date			$ 573,800,000