Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Asset Retirement Obligations [Abstract]
ARO liability, January 1:	$ 96,446		$ 69,265
Accretion of discount	1,101		874
Liability incurred	1,204		1,559
Liability settled	(1,052)		(359)
Revision of estimates	(5,050)	[1]	(1)
ARO liability, March 31:	92,649		71,338
Less current portion	2,904		1,836
Total long-term plugging liability	$ 89,745		$ 69,502

[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.