Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Asset Retirement Obligation Disclosure [Abstract]
ARO liability, January 1:		$ 69,444	$ 70,170
Accretion of discount		1,829	2,112
Liability incurred		244	1,123
Liability settled		(3,907)	(1,350)
Liability sold		(105)	(1,563)
Revision of estimates	[1]	(4,778)	4,993
ARO liability, September 30:		62,727	75,485
Less current portion		1,451	2,947
Total long-term ARO		$ 61,276	$ 72,538

[1] Plugging liability estimates were revised in both 2018 and 2017 for updates in the cost of services used to plug wells over the preceding year. We had various upward and downward adjustments.