Property, Plant And Equipment (Aging of Capitalized Exploratory Well Costs) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($) item	Sep. 30, 2015 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 128,156	$ 209,652	$ 130,514	$ 120,455
No. of Wells	11	13
No. of Projects	5	6
Zero to One Year [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 10,563	$ 52,249
No. of Wells	2	5
No. of Projects	2	3
One to Two Years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 53,101	$ 32,192
No. of Wells	3	2
No. of Projects	3	1
Two to Three Years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 31,627	$ 27,842
No. of Wells	2	2
Three Years or More [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 32,865	$ 97,369
No. of Wells	4	4
No. of Projects		2