Long-Term Debt Revolving Credit Facility (Details) $ in Thousands		6 Months Ended
		Jun. 30, 2017 USD ($)	Jul. 26, 2017 USD ($)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Long-term Line of Credit, Noncurrent		$ 0		$ 0
Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		2,500,000
Line of Credit Facility, Current Borrowing Capacity		925,000		1,165,000
Accelerated Amortization of Debt Issuance Costs Related To Borrowing Base And Lender Commitment Revisions		1,100
Long-term Line of Credit, Noncurrent	[1]	0		0
Letters of Credit Outstanding, Amount	[2]	200		200
Line of Credit Facility, Remaining Borrowing Capacity		924,800		1,164,800
Unamortized Debt Issuance Expense		$ 3,900		$ 5,900
Maximum [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Covenant Compliance, Senior Secured Debt To Adjusted EBITDAX Ratio		2.75
Minimum [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Covenant Compliance, Adjusted Current Ratio		1.0
Debt Instrument, Covenant Compliance, Adjusted EBITDAX To Interest Expense		2.0
Subsequent Event [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity			$ 925,000
Long-term Line of Credit, Noncurrent			0
Letters of Credit Outstanding, Amount	[2]		200
Line of Credit Facility, Remaining Borrowing Capacity			$ 924,800

[1] Unamortized deferred financing costs attributable to the credit facility are presented as a component of other noncurrent assets on the accompanying balance sheets and totaled $3.9 million and $5.9 million as of June 30, 2017, and December 31, 2016, respectively.

[2] Letters of credit outstanding reduce the amount available under the credit facility on a dollar-for-dollar basis.