Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
ARO liability, January 1:		$ 69,444	$ 70,170
Accretion of discount		659	785
Liability incurred		118	658
Liability settled		(1,626)	(630)
Liability sold		(81)	(432)
Revision of estimates	[1]	(4,751)	(508)
ARO liability, March 31:		63,763	70,043
Less current portion		1,477	3,243
Total long-term ARO		$ 62,286	$ 66,800

[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.