Property, Plant And Equipment (Net Changes in Capitalized Exploratory Well Costs) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Property, Plant And Equipment [Abstract]
Beginning balance at January 1	$ 130,514	$ 120,455
Additions pending the determination of proved reserves	800	1,620
Other adjustments	(3,205)
Balance at June 30	$ 128,109	$ 122,075