Oil And Natural Gas Properties And Related Equipment (Gathering and Transportation Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Gathering and transportation assets	$ 152,209	$ 147,479
Less: Accumulated depreciation, depletion, amortization and impairments	(674,338)	(652,167)
Midstream
Property, Plant and Equipment [Line Items]
Gathering and transportation assets	152,209	147,479
Less: Accumulated depreciation, depletion, amortization and impairments	(15,020)	(1,402)
Total gathering and transportation assets	$ 137,189	$ 146,077