Property, Plant And Equipment (Aging of Capitalized Exploratory Well Costs) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($) item	Dec. 31, 2013 USD ($) item	Dec. 31, 2012 USD ($)
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 130,514,000	$ 120,455,000	$ 393,030,000	$ 445,697,000
No. of Wells	13	8	32
No. of Projects	6	3	9
Zero to One Year [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 66,032,000		$ 56,499,000
No. of Wells	7		3
No. of Projects	6		1
One to Two Years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $		$ 59,330,000	$ 60,787,000
No. of Wells		3	7
No. of Projects		1	1
Two to Three Years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 57,876,000	$ 6,606,000
No. of Wells	3	3
Three Years or More [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 6,606,000	$ 54,519,000	$ 275,744,000
No. of Wells	3	2	22
No. of Projects		2	7