Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Asset Retirement Obligations [Abstract]
ARO liability, January 1:	$ 69,265		$ 56,404
Accretion of discount	3,838		2,937
Liability incurred	15,068	[1]	4,768
Liability settled	(1,009)		(763)
Revision of estimates	9,284	[2]	5,919	[2]
ARO liability, December 31:	96,446		69,265
Less current portion	3,040		1,915
Total long-term ARO liability	$ 93,406		$ 67,350

[1] Liability incurred in 2011 includes new wells acquired.

[2] Plugging liability estimates were revised upward in both 2011 and 2010 due to increases in the cost of services used to plug wells over the preceding years.