Property, Plant And Equipment (Aging of Capitalized Exploratory Well Costs) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) item	Mar. 31, 2015 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 129,628	$ 120,596	$ 130,514	$ 120,455
No. of Wells	13	8
No. of Projects	6	3
Zero to One Year [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 65,136
No. of Wells	7
No. of Projects	6
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	$ 33,744
No. of Wells	2	4
No. of Projects		2
Three Years or More [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount | $	$ 32,865	$ 54,660
No. of Wells	4	2