Property, Plant And Equipment (Aging of Capitalized Exploratory Well Costs) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) item	Sep. 30, 2014 USD ($) item	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 209,652	$ 406,625	$ 120,455	$ 393,030
No. of Wells	13	32
No. of Projects	6	9
Zero to one year [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 52,249	$ 32,192
No. of Wells	5	2
No. of Projects	3	1
One to two years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 32,192	$ 36,676
No. of Wells	2	2
No. of Projects	1	1
Two to three years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 27,842	$ 51,898
No. of Wells	2	6
Three years or more [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 97,369	$ 285,859
No. of Wells	4	22
No. of Projects	2	7