Long-term Debt Revolving Credit Facility (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2015 USD ($)	Feb. 17, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Line of Credit Facility [Line Items]
Percentage of Proved Oil and Gas Properties Secured for Credit Facility Borrowing		75.00%
Line of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	[1]	$ 202,000			$ 166,000
Letters of Credit Outstanding, Amount	[2]	200			808
Line of Credit Facility, Remaining Borrowing Capacity		$ 1,297,800			$ 1,333,192
Line of Credit [Member] | Borrowing Base Utilization of 25 Percent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.30%
Line of Credit [Member] | Borrowing Base Utilization Of More Than 25 Percent But Less Than 50 Percent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.30%
Line of Credit [Member] | Borrowing Base Utilization Of More Than 50 Percent But Less Than 75 Percent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.35%
Line of Credit [Member] | Borrowing Base Utilization Of More Than 75 Percent But Less Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.375%
Line of Credit [Member] | Borrowing Base Utilization Of More Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.375%
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		1,500,000
Borrowing Base, Line of Credit		$ 2,000,000		$ 2,400,000
Subsequent Event [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Long-term Line of Credit	[1]		$ 243,000
Letters of Credit Outstanding, Amount	[2]		200
Line of Credit Facility, Remaining Borrowing Capacity			$ 1,256,800
Eurodollar [Member] | Line of Credit [Member] | Borrowing Base Utilization of 25 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.25%
Eurodollar [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 25 Percent But Less Than 50 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Eurodollar [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 50 Percent But Less Than 75 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.75%
Eurodollar [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 75 Percent But Less Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.00%
Eurodollar [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.25%
Debt Instrument Variable Rate, Alternative Base Rate, And Swingline Loans [Member] | Line of Credit [Member] | Borrowing Base Utilization of 25 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		0.25%
Debt Instrument Variable Rate, Alternative Base Rate, And Swingline Loans [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 25 Percent But Less Than 50 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		0.50%
Debt Instrument Variable Rate, Alternative Base Rate, And Swingline Loans [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 50 Percent But Less Than 75 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		0.75%
Debt Instrument Variable Rate, Alternative Base Rate, And Swingline Loans [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 75 Percent But Less Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.00%
Debt Instrument Variable Rate, Alternative Base Rate, And Swingline Loans [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.25%
Maximum [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument Covenant Compliance Debt To Adjusted EBITDAX Ratio		4.0
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

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