Supplemental Information On Oil And Natural Gas Producing Activities (Change Standardized Measure) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Supplemental Information On Oil And Natural Gas Producing Activities
Beginning of the period	$ 67,852	$ 119,533
Sales and transfers of oil and natural gas, net of production costs	(8,700)	(30,748)
Net changes in prices and production costs related to future production	(7,868)	(125,979)
Changes in development costs	5,040	5,016
Changes in extensions and discoveries		178
Revisions of previous quantity estimates	(17,924)	(11,299)
Purchases and sales of reserves in place	9,134	109,181
Accretion discount	6,175	11,953
Change in production rates, timing, and other	(4,073)	(9,983)
Standardized measure of discount future net cash flows related to proved gas reserves	$ 49,636	$ 67,852