Supplemental Information on Oil and Natural Gas Properties (unaudited) (Narrative) (Details) MBoe in Thousands, $ in Thousands	2 Months Ended	12 Months Ended
	Feb. 23, 2018 item	Dec. 31, 2017 USD ($) item MBoe $ / Boe	Dec. 31, 2016 USD ($) item MBoe $ / Boe	Dec. 31, 2015 USD ($) item MBoe $ / Boe	Dec. 31, 2014 MBoe
Reserve Quantities [Line Items]
Depletion expense per physical unit of production | $ / Boe		13.82	12.81	19.74
Lease operating expense per physical unit of production | $ / Boe		5.96	6.88	7.71
Proved developed and undeveloped reserve, net (energy) | MBoe		136,974	91,580	54,271	32,824
Proved developed and proved undeveloped reserves, percentage change between periods		50.00%	69.00%	65.00%
Period to convert the PUDs into proved developed reserves		5 years
Proved undeveloped reserves, percentage change between periods		40.00%	88.00%	75.00%
Proved undeveloped reserves | MBoe		67,656	48,348	25,654	14,623
Proved undeveloped reserves reclassification to proved developed production | MBoe		(8,281)	6,823
Proved undeveloped reserves conversion to proved developed reserves, percentage transferred		(17.00%)	27.00%
Disposed of by Sale
Reserve Quantities [Line Items]
Proved developed and undeveloped reserve period increase (decrease) | MBoe			11,168
Permian Basin [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserve period increase (decrease) | MBoe		57,881	48,477
Number of wells drilled during the period | item		49	29	36
Number of wells drilled during the period, net | item		38.2	20.9	27.1
Removal of proved undeveloped locations | item		13
Proved undeveloped reserves reclassification to proved developed production | MBoe				2,742
Proved undeveloped reserves conversion to proved developed reserves, percentage transferred				19.00%
Proved undeveloped reserves conversion to proved developed reserves total cost | $		$ 57,019	$ 43,415	$ 55,933
Permian Basin [Member] | Continued Horizontal Development [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserve period increase (decrease) | MBoe		30,198	12,035	13,774
Permian Basin [Member] | Acquisitions Net of Divestitures [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserve period increase (decrease) | MBoe		3,267	17,482
Permian Basin [Member] | Removal of Locations [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserve period increase (decrease) | MBoe		(5,876)
Subsequent Event
Reserve Quantities [Line Items]
Number of horizontal wells drilled gross | item	8
Number of horizontal wells drilled net | item	6.0
Number of completed horizontal wells gross | item	5
Number of completed horizontal wells net | item	3.0
Number of horizontal wells in progress gross | item	3
Number of horizontal wells in progress net | item	3.0