Acquisitions and Divestitures (Details Textuals) (USD $)	12 Months Ended			0 Months Ended		9 Months Ended	1 Months Ended	3 Months Ended		1 Months Ended			12 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 27, 2013 Cedar Creek Anticline [Member]		Dec. 31, 2013 Cedar Creek Anticline [Member]	Jan. 31, 2013 Cedar Creek Anticline [Member] Scenario, Plan [Member]	Dec. 31, 2012 Bakken Exchange Transaction [Member] Rate		Jun. 30, 2012 Thompson Field [Member] Rate		Apr. 30, 2012 Paradox Basin [Member]	Dec. 31, 2012 Paradox Basin [Member]	Feb. 29, 2012 Non-core Gulf Coast Assets [Member]	Dec. 31, 2012 Non-core Gulf Coast Assets [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross				$ 1,001,707,000	[1]		$ 1,050,000,000			$ 366,179,000	[1]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual						268,300,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual						194,200,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents								1,277,041,000	[2]
Percent of Overriding Royalty Interest in CO2 Properties Acquired 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
Proceeds from sale of oil and natural gas properties and equipment	8,037,000	34,750,000	69,370,000									68,500,000		141,800,000
Gain (Loss) on Sale of Property													$ 0		$ 0

[1] See Note 6, Income Taxes, for additional information regarding the like-kind-exchange transaction utilized to fund this purchase and Note 13, Supplemental Cash Flow Information, for supplemental cash flow information regarding the cash payment.

[2] See Note 13, Supplemental Cash Flow Information, for additional information regarding the placement of $1.05 billion of the proceeds in a qualified trust in order to enable a like-kind exchange transaction for federal income tax purposes.