Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012
Asset Retirement Obligation Disclosure [Abstract]
ARO liability, January 1:	$ 146,159		$ 96,446
Accretion of discount	2,825		2,126
Liability incurred	2,869		4,420
Liability settled	(3,516)		(1,447)
Revision of estimates	(11,298)	[1]	(5,022)	[1]
ARO liability, June 30:	137,039		96,523
Less current portion	2,948		2,909
Total long-term ARO	$ 134,091		$ 93,614

[1] Plugging liability estimates were revised in both 2013 and 2012 for updates in the cost of services used to plug wells over the preceding year. We had various upward and downward adjustments as well as changes in estimated timing of cash flows.