Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011
Asset Retirement Obligation Disclosure [Abstract]
ARO liability, January 1:	$ 96,446		$ 69,265
Accretion of discount	2,126		1,735
Liability incurred	4,420		2,879
Liability settled	(1,447)		(666)
Revision of estimates	(5,022)	[1]	9
ARO liability, June 30:	96,523		73,222
Less current portion	2,909		1,781
Total long-term plugging liability	$ 93,614		$ 71,441

[1] 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.