Revenue Recognition - Revenue Disaggregated and Reconciles Disaggregated Revenue to Revenue Reported (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2017		Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Net commodity sales	$ 65,519	$ 75,947		$ 157,803		$ 181,835
Oil
Disaggregation of Revenue [Line Items]
Net commodity sales	46,576					132,378
Natural gas
Disaggregation of Revenue [Line Items]
Net commodity sales	9,458					26,584
Natural gas liquids
Disaggregation of Revenue [Line Items]
Net commodity sales	14,078					34,789
Gross commodity sales
Disaggregation of Revenue [Line Items]
Net commodity sales	70,112					193,751
Transportation and processing
Disaggregation of Revenue [Line Items]
Cost of goods sold	$ 4,593	$ 2,942	[1]	$ 6,370	[1]	$ 11,916

[1] See “Note 5—Revenue recognition.”