Supplementary Oil And Gas Information (Twelve Month Average Trailing Prices) (Details)	12 Months Ended
	Dec. 31, 2017 $ / bbl $ / MMBTU CAD / bbl CAD / MMBTU	Dec. 31, 2016 $ / bbl $ / MMBTU CAD / bbl CAD / MMBTU	Dec. 31, 2015 $ / bbl $ / MMBTU CAD / bbl CAD / MMBTU
Oil and NGLs [Member] | WTI [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Reference Price | $ / bbl	51.34	42.75	50.28
Oil and NGLs [Member] | Edmonton Condensate [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Reference Price | CAD / bbl	67.65	55.39	61.94
Natural Gas [Member] | Henry Hub [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Reference Price | $ / MMBTU	2.98	2.49	2.58
Natural Gas [Member] | AECO [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Reference Price | CAD / MMBTU	2.32	2.17	2.69