Property, Plant And Equipment (Aging of Capitalized Exploratory Well Costs) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) item	Jun. 30, 2015 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 128,109	$ 122,075	$ 130,514	$ 120,455
No. of Wells	11	10
No. of Projects	5	4
Zero to One Year [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 63,617	$ 217
No. of Wells	5	2
No. of Projects	5	1
One to Two Years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $		$ 32,192
No. of Wells		2
No. of Projects		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	$ 61,824
No. of Wells	4	4
No. of Projects		2