Property and Equipment, Net (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) $ / Boe	Mar. 31, 2016 USD ($) $ / Boe
Property, Plant and Equipment [Line Items]
Average depreciation, depletion and amortization, per Boe | $ / Boe	12.69	15.22
Internal costs capitalized, Oil and Gas producing activities	$ 5,400	$ 4,400
Capitalized interest	3,800	5,600
Proceeds from sales of oil and gas properties, net	$ 17,372	$ 1,785
Reserves discount factor	10.00%
Delaware Basin [Member]
Property, Plant and Equipment [Line Items]
Proceeds from sales of oil and gas properties, net	$ 15,300