Debt (New Revolver) (Details) - New Revolver	9 Months Ended
	Sep. 30, 2017 USD ($)
Line Of Credit Facility [Line Items]
Borrowing base amount	$ 400,000,000
Debt instrument maturity date	Mar. 21, 2021
Initial borrowing base amount	$ 225,000,000
Debt instrument redetermination date	May 01, 2018
Availability under the facility	$ 71,172,000
Commitment fee on unused portion of the borrowing base	0.50%
Letter of Credit
Line Of Credit Facility [Line Items]
Basis spread on variable rate	0.125%
Alternate Base Rate
Line Of Credit Facility [Line Items]
Additional interest rate on outstanding amounts in event of default	2.00%
Alternate Base Rate | Minimum
Line Of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Alternate Base Rate | Maximum
Line Of Credit Facility [Line Items]
Basis spread on variable rate	3.00%
Adjusted LIBO Rate
Line Of Credit Facility [Line Items]
One month interest period	1 month
Two month interest period	2 months
Three month interest period	3 months
Six month interest period	6 months
Outstanding borrowings, accruing weighted average interest rate	4.78%
Adjusted LIBO Rate | Minimum
Line Of Credit Facility [Line Items]
Basis spread on variable rate	3.00%
Adjusted LIBO Rate | Maximum
Line Of Credit Facility [Line Items]
Basis spread on variable rate	4.00%