Supplemental Information On Oil And Natural Gas Producing Activities (Standardized Measure) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Information On Oil And Natural Gas Producing Activities
Future cash inflows	$ 197,739	$ 182,612
Future production costs	(101,300)	(102,569)
Future estimated development costs	(4,346)	(8,872)
Future net cash flows	92,093	71,171
10% annual discount for estimated timing of cash flows	(35,396)	(21,535)
Standardized measure of discounted estimated future net cash flows related to proved oil and natural gas reserves	$ 56,697	$ 49,636	$ 67,852