Supplemental Information On Oil And Natural Gas Producing Activities (Standardized Measure) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Information On Oil And Natural Gas Producing Activities
Future cash inflows	$ 144,628	$ 186,675
Future production costs	(80,007)	(99,187)
Future estimated development costs	(3,400)	(4,043)
Future net cash flows	61,221	83,445
10% annual discount for estimated timing of cash flows	(22,871)	(31,199)
Standardized measure of discounted estimated future net cash flows related to proved oil and natural gas reserves	$ 38,350	$ 52,246	$ 56,697