Property, Plant And Equipment (Net Changes in Capitalized Exploratory Well Costs) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Property, Plant And Equipment [Abstract]
Beginning balance at January 1	$ 130,514	$ 120,455
Additions pending the determination of proved reserves	847	89,197
Other adjustments	(3,205)
Balance at September 30	$ 128,156	$ 209,652