Derivative Instruments and Fair Value Measurements - Narrative (Details) - Commodity Contract	6 Months Ended	12 Months Ended
	Jun. 30, 2018 barrelOfOilPerDay contract	Dec. 31, 2017 barrelOfOilPerDay contract
Derivative Instruments, Gain (Loss) [Line Items]
Number of contracts held | contract	16	20
Reported Value Measurement
Derivative Instruments, Gain (Loss) [Line Items]
Number of contracts held | contract	4	4
July 2018
Derivative Instruments, Gain (Loss) [Line Items]
Production	646	646
August through September 2018
Derivative Instruments, Gain (Loss) [Line Items]
Production	322	322
October through December 2018
Derivative Instruments, Gain (Loss) [Line Items]
Production	258	258
January 2019 through April 2019
Derivative Instruments, Gain (Loss) [Line Items]
Production	322
May 2019
Derivative Instruments, Gain (Loss) [Line Items]
Production	258
January 2018
Derivative Instruments, Gain (Loss) [Line Items]
Production		452
February through May 2018
Derivative Instruments, Gain (Loss) [Line Items]
Production		322
June 2018
Derivative Instruments, Gain (Loss) [Line Items]
Production		258