Acquisitions and Divestitures (Details Textuals) (USD $)	6 Months Ended					1 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Mar. 27, 2013		Dec. 31, 2012	Jun. 30, 2012 Thompson Field [Member] Rate	Feb. 29, 2012 Non-core Gulf Coast Assets [Member]	Jun. 30, 2012 Non-core Gulf Coast Assets [Member]	Apr. 30, 2012 Paradox Basin [Member]	Jun. 30, 2012 Paradox Basin [Member]	Dec. 31, 2012 Bakken Exchange Transaction [Member] Rate	Jan. 31, 2013 Cedar Creek Anticline [Member]	Jun. 30, 2013 Cedar Creek Anticline [Member]	Jun. 30, 2013 Cedar Creek Anticline [Member]
Acquisitions and Divestitures (Textuals) [Abstract]
Anticipated purchase price of oil and natural gas properties												$ 1,050,000,000
Business Acquisition, Cost of Acquired Entity, Cash Paid			988,982,000	[1]		366,200,000
Proceeds from Delayed Tax Exempt Exchange											1,050,000,000
Restricted cash	0				1,050,015,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual													88,700,000	92,700,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual													65,200,000	67,900,000
Business Acquisition, Purchase Price Allocation, Current Assets, Cash and Cash Equivalents											1,300,000,000
Overriding Royalty Interest Obtained In A Business Acquisition											33.33%
Net working interest acquired in purchase of oil and natural gas properties						100.00%
Net revenue interest acquired in purchase of oil and natural gas properties						84.70%
Net Revenue Interest Retained By Seller						5.00%
Oil Production Threshold (in Bbls/d)						3,000
Anticipated Proceeds From Sale Of Oil And Natural Gas Properties									75,000,000
Proceeds from Sale of Oil and Gas Property and Equipment	5,496,000	32,302,000					141,800,000		68,500,000
Gain (Loss) on Sale of Property								$ 0		$ 0

[1] This cash payment was made through a qualified intermediary from cash placed in qualifying trust accounts from a portion of the proceeds received from the Bakken Exchange Transaction (as defined below) in order to enable a like-kind-exchange transaction for federal income tax purposes. As such, this amount is not reflected as a cash payment to purchase oil and natural gas properties in our Unaudited Condensed Consolidated Statement of Cash Flows.