Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]
ARO liability, January 1:		$ 70,170	$ 98,297
Accretion of discount		2,886	2,779
Liability incurred		1,948	584
Liability settled		(2,694)	(1,215)
Liability sold		(1,735)	(10,882)
Revision of estimates	[1]	(1,131)	(19,393)
ARO liability, December 31:		69,444	70,170
Less current portion		1,726	2,906
Total long-term ARO liability		$ 67,718	$ 67,264

[1] 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 and changes in estimated timing of cash flows.