Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
ARO liability, January 1:	$ 96,446		$ 69,265
Accretion of discount	4,615		3,838
Liability incurred	56,650	[1]	15,068
Liability settled	(2,788)		(1,009)
Liability Sold	(1,258)		0
Revision of estimates	(7,506)	[2]	9,284
ARO liability, December 31:	146,159		96,446
Less current portion	2,953		3,040
Total long-term ARO liability	143,206		93,406
Noble Energy, Inc. [Member]
Liability incurred	$ 46,700

[1] The liability incurred increased $46.7 million related to the Noble properties acquired in September 2012.

[2] Plugging liability estimates were revised in March 2012 for updates in the cost of services used to plug wells over the preceding year. Although cost per well increased, a slight decrease in the inflation factor resulted in a decrease in estimated cost. Costs were reviewed each quarter resulting in no change to the March 2012 estimates.