Property, Plant And Equipment (Schedule Of Charges For Impairment) (Details) (USD $)	3 Months Ended				12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Impairment expense					$ 1,863,000	$ 2,625,928,000	$ 107,059,000
U.S. [Member]
Impairment expense	451,500,000	479,900,000	1,042,700,000	178,000,000	1,809,000	2,152,665,000	0
Canada [Member]
Impairment expense	102,800,000	66,300,000	157,000,000	139,900,000	0	465,935,000	49,063,000
Oil and Gas Properties [Member] | U.S. [Member]
Impairment expense					0	2,152,128,000	0
Oil and Gas Properties [Member] | Canada [Member]
Impairment expense					0	465,935,000	49,063,000
Midstream Operations [Member] | Other Property and Equipment [Member] | U.S. [Member]
Impairment expense					54,000	7,328,000	57,996,000
Exploration and Production Equipment [Member] | Other Property and Equipment [Member] | U.S. [Member]
Impairment expense					$ 1,809,000	$ 537,000	$ 0