Asset Retirement Obligations (Schedule Of Asset Retirement Obligations) (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017
Asset Retirement Obligation Disclosure [Abstract]
ARO liability, January 1:		$ 69,444	$ 70,170
Accretion of discount		1,248	1,458
Liability incurred		211	1,018
Liability settled		(3,142)	(1,224)
Liability sold		(94)	(1,412)
Revision of estimates	[1]	(4,829)	39
ARO liability, June 30:		62,838	70,049
Less current portion		1,451	2,825
Total long-term ARO		$ 61,387	$ 67,224

[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.