Supplemental Oil And Gas Disclosures (Schedule Of The Oil And Natural Gas Property Costs Not Being Amortized) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Unproved properties acquired and wells in progress	$ 314,867	$ 337,099	$ 485,568
2016
Unproved properties acquired and wells in progress	23,494
2015
Unproved properties acquired and wells in progress	41,445
2014
Unproved properties acquired and wells in progress	55,562
2013 and prior
Unproved properties acquired and wells in progress	$ 194,366