Long-Term Debt Revolving Credit Facility (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2015	Jul. 22, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term Line of Credit		$ 122,000		$ 166,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		2,500,000
Line of Credit Facility, Current Borrowing Capacity		1,500,000
Borrowing Base, Line of Credit		$ 2,400,000
Percentage of Proved Property Secured for Credit Facility Borrowing		75.00%
Line of Credit, Covenant Compliance, Maximum Annual Dividend Payment		$ 50,000
Long-term Line of Credit		122,000		166,000
Letters of Credit Outstanding, Amount	[1]	200		808
Line of Credit Facility, Remaining Borrowing Capacity		$ 1,377,800		$ 1,333,192
Subsequent Event [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Line of Credit			$ 175,000
Letters of Credit Outstanding, Amount	[1]		200
Line of Credit Facility, Remaining Borrowing Capacity			$ 1,324,800

[1] (1) Letters of credit reduce the amount available under the credit facility on a dollar-for-dollar basis.