Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016
Asset Retirement Obligation Disclosure [Abstract]
ARO liability, January 1:		$ 70,170	$ 98,297
Accretion of discount		2,112	2,147
Liability incurred		1,123	311
Liability settled		(1,350)	(874)
Liability sold	[1]	(1,563)	(10,758)
Revision of estimates	[2]	4,993	(18,102)
ARO liability, September 30:		75,485	71,021
Less current portion		2,947	3,498
Total long-term ARO		$ 72,538	$ 67,523

[1] We sold our interest in a number of non-core wells to unaffiliated third-parties during the first nine months of 2017 and 2016, respectively.

[2] Plugging liability estimates were revised in both 2017 and 2016 for updates in the cost of services used to plug wells over the preceding year. We had various upward and downward adjustments.