Long-Term Debt Revolving Credit Facility (Details) $ in Thousands		9 Months Ended
		Sep. 30, 2018 USD ($)	Oct. 24, 2018 USD ($)	Dec. 31, 2017 USD ($)
Line of Credit Facility [Line Items]
Credit facility balance		$ 0		$ 0
Line of Credit [Member] | Borrowing Base Utilization Of Less Than 25 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 Less Than 25 Percent [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Line of Credit [Member] | Borrowing Base Utilization Of Less Than 25 Percent [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		0.50%
Line of Credit [Member] | Borrowing Base Utilization Of 25 Percent Or More But Less Than 50 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 25 Percent Or More But Less Than 50 Percent [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.75%
Line of Credit [Member] | Borrowing Base Utilization Of 25 Percent Or More But Less Than 50 Percent [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		0.75%
Line of Credit [Member] | Borrowing Base Utilization Of 50 Percent Or More But Less Than 75 Percent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.50%
Line of Credit [Member] | Borrowing Base Utilization Of 50 Percent Or More But Less Than 75 Percent [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.00%
Line of Credit [Member] | Borrowing Base Utilization Of 50 Percent Or More But Less Than 75 Percent [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.00%
Line of Credit [Member] | Borrowing Base Utilization Of 75 Percent Or More But Less Than 90 Percent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.50%
Line of Credit [Member] | Borrowing Base Utilization Of 75 Percent Or More But Less Than 90 Percent [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.25%
Line of Credit [Member] | Borrowing Base Utilization Of 75 Percent Or More But Less Than 90 Percent [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.25%
Line of Credit [Member] | Borrowing Base Utilization Of 90 Percent Or More [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage		0.50%
Line of Credit [Member] | Borrowing Base Utilization Of 90 Percent Or More [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		2.50%
Line of Credit [Member] | Borrowing Base Utilization Of 90 Percent Or More [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Line of Credit [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, maximum loan amount		$ 2,500,000
Line of credit facility, current borrowing base		1,500,000
Line of credit agreement, aggregate lender commitments		1,000,000		925,000
Credit facility balance	[1]	0		0
Letters of credit	[2]	200		200
Available borrowing capacity		999,800		924,800
Unamortized deferred financing costs		$ 6,700		$ 3,100
Line of Credit [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Line of credit agreement, aggregate lender commitments			$ 1,000,000
Credit facility balance			0
Letters of credit	[2]		200
Available borrowing capacity			$ 999,800
Line of Credit [Member] | Revolving Credit Facility [Member] | Maximum [Member] | 12/31/18 QE through 12/31/19 QE [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Covenant Compliance, Total Funded Debt To Adjusted EBITDAX Ratio		4.25
Line of Credit [Member] | Revolving Credit Facility [Member] | Maximum [Member] | 3/31/20 QE and Thereafter [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Covenant Compliance, Total Funded Debt To Adjusted EBITDAX Ratio		4.00
Line of Credit [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Covenant Compliance, Adjusted Current Ratio		1.0

[1] (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 $6.7 million and $3.1 million as of September 30, 2018, and December 31, 2017, respectively. These costs are being amortized over the term of the credit facility on a straight-line basis.

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