Property And Equipment, Net (Schedule Of Property And Equipment) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Proved properties	$ 5,744,434	$ 5,615,153
Accumulated depreciation, depletion and amortization and impairments	(3,784,483)	(3,649,806)
Proved properties, net	1,959,951	1,965,347
Unproved properties, not being amortized
Unevaluated leasehold and seismic costs	539,836	612,589
Capitalized interest	58,056	47,698
Total unproved properties, not being amortized	597,892	660,287
Other property and equipment	27,223	25,625
Accumulated depreciation	(16,641)	(15,449)
Other property and equipment, net	10,582	10,176
Total property and equipment, net	$ 2,568,425	$ 2,635,810