Long-Term Debt Revolving Credit Facility (Details) $ in Thousands		3 Months Ended
		Sep. 30, 2016 USD ($)	Oct. 26, 2016 USD ($)	Oct. 04, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Percentage of Proved Property Secured for Credit Facility Borrowing		90.00%
Long-term Line of Credit, Noncurrent		$ 0				$ 202,000
Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Borrowing Base, Line of Credit		1,110,000			$ 1,250,000
Line of Credit Facility, Current Borrowing Capacity		1,106,875			$ 1,250,000	1,500,000
Percentage of Proved Property Secured for Credit Facility Borrowing					90.00%
Debt Issuance Costs, Gross					$ 3,100
Line of Credit Facility, Maximum Borrowing Capacity		2,500,000
Long-term Line of Credit, Noncurrent	[1]	0				202,000
Letters of Credit Outstanding, Amount	[2]	200				200
Line of Credit Facility, Remaining Borrowing Capacity		$ 1,106,675				$ 1,297,800
Borrowing Base Utilization Of 25 Percent Or Less [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.30%
Borrowing Base Utilization Of 25 Percent Or Less [Member] | Eurodollar [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.75%
Borrowing Base Utilization Of 25 Percent Or Less [Member] | Prime Rate [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		0.75%
Borrowing Base Utilization Of More Than 25 Percent But Less Than 50 Percent [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.30%
Borrowing Base Utilization Of More Than 25 Percent But Less Than 50 Percent [Member] | Eurodollar [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.00%
Borrowing Base Utilization Of More Than 25 Percent But Less Than 50 Percent [Member] | Prime Rate [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.00%
Borrowing Base Utilization Of More Than 50 Percent But Less Than 75 Percent [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.35%
Borrowing Base Utilization Of More Than 50 Percent But Less Than 75 Percent [Member] | Eurodollar [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.25%
Borrowing Base Utilization Of More Than 50 Percent But Less Than 75 Percent [Member] | Prime Rate [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.25%
Borrowing Base Utilization Of More Than 75 Percent But Less Than 90 Percent [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.375%
Borrowing Base Utilization Of More Than 75 Percent But Less Than 90 Percent [Member] | Eurodollar [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.50%
Borrowing Base Utilization Of More Than 75 Percent But Less Than 90 Percent [Member] | Prime Rate [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Borrowing Base Utilization Of More Than 90 Percent [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.375%
Borrowing Base Utilization Of More Than 90 Percent [Member] | Eurodollar [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.75%
Borrowing Base Utilization Of More Than 90 Percent [Member] | Prime Rate [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.75%
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]
Borrowing Base, Line of Credit				$ 1,350,000
Line of Credit Facility, Current Borrowing Capacity				$ 1,250,000
Long-term Line of Credit, Noncurrent	[1]		$ 0
Letters of Credit Outstanding, Amount	[2]		200
Line of Credit Facility, Remaining Borrowing Capacity			$ 1,249,800

[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 thus are not deducted from the credit facility balance.

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