Supplemental Oil And Gas Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017 item $ / bbl	Dec. 31, 2016 item $ / bbl	Dec. 31, 2015 item $ / bbl	Dec. 31, 2014 item
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Proved undeveloped reserve locations | item	3	0	0	27
Barrel Of Oil [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Price | $ / bbl	45.83	37.35	43.98