Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011
Asset Retirement Obligation Disclosure [Abstract]
ARO liability, January 1:	$ 96,446		$ 69,265
Accretion of discount	3,215		2,598
Liability incurred	52,306	[1]	12,674
Liability settled	(1,606)		(831)
Liability Sold	1,258		0
Revision of estimates	(4,254)	[2]	9,096
ARO liability, September 30:	144,849		92,802
Less current portion	2,857		2,074
Total long-term ARO	$ 141,992		$ 90,728

[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 again reviewed in September 2012 resulting in no change to the March 2012 estimates.