Supplemental Oil And Gas Disclosures (Standardized Measure Of Discounted Future Cash Flows Relating To Proved Reserves Disclosure) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Net Cash Flows [Abstract]
Future cash flows	$ 3,347,396	$ 2,030,925	$ 2,475,898
Future production costs	(1,308,244)	(861,625)	(1,017,777)
Future development costs	(369,560)	(173,446)	(228,445)
Future income tax expenses	(234,152)	(141,752)	(230,544)
Future net cash flows	1,435,440	854,102	999,132
10% annual discount for estimated timing of cash flows	(628,270)	(335,892)	(409,646)
Standardized measure of discounted future net cash flows relating to proved oil, NGLs and natural gas reserves	$ 807,170	$ 518,210	$ 589,486	$ 1,435,744
Percentage of annual discount for estimated timing of cash flows	10.00%	10.00%	10.00%