Long-term Debt Revolving Credit Facility (Details)		12 Months Ended
		Dec. 31, 2017 USD ($)	Feb. 14, 2018 USD ($)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Credit facility balance		$ 0		$ 0
Line of Credit [Member] | Borrowing Base Utilization of 25 Percent [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, unused capacity, commitment fee rate		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 agreement, unused capacity, commitment fee rate		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 agreement, unused capacity, commitment fee rate		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 agreement, unused capacity, commitment fee rate		0.375%
Line of Credit [Member] | Borrowing Base Utilization Of More Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, unused capacity, commitment fee rate		0.375%
Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, maximum loan amount		$ 2,500,000,000
Line of credit agreement, aggregate lender commitment amount		925,000,000		1,165,000,000
Credit facility balance	[1]	0		0
Letters of credit outstanding, amount	[2]	200,000		200,000
Available borrowing capacity		924,800,000		1,164,800,000
Unamortized deferred financing costs		$ 3,100,000		$ 5,900,000
Subsequent Event [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, aggregate lender commitment amount			$ 925,000,000
Credit facility balance	[1]		0
Letters of credit outstanding, amount	[2]		200,000
Available borrowing capacity			$ 924,800,000
Eurodollar [Member] | Line of Credit [Member] | Borrowing Base Utilization of 25 Percent [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, basis spread on variable rate		1.75%
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]
Line of credit agreement, basis spread on variable rate		2.00%
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]
Line of credit agreement, basis spread on variable rate		2.25%
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]
Line of credit agreement, basis spread on variable rate		2.50%
Eurodollar [Member] | Line of Credit [Member] | Borrowing Base Utilization Of More Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, basis spread on variable rate		2.75%
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]
Line of credit agreement, 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 25 Percent But Less Than 50 Percent [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, 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 50 Percent But Less Than 75 Percent [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, basis spread on variable rate		1.25%
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]
Line of credit agreement, basis spread on variable rate		1.50%
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]
Line of credit agreement, basis spread on variable rate		1.75%
Maximum [Member] | Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, 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]
Line of credit agreement, covenant compliance, adjusted current ratio		1.0
Line of credit agreement, covenant compliance, adjusted EBITDAX to interest expense ratio		2.0

[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 $3.1 million and $5.9 million as of December 31, 2017, and 2016, respectively.

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