Suspended Well Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($) project	Dec. 31, 2014 USD ($) project	Dec. 31, 2013 USD ($) project
Reconciliation of capitalized exploratory well costs on completed wells
Beginning balance	$ 226,714	$ 376,166	$ 372,492
Additions to capitalized exploratory well costs pending the determination of proved reserves	223,542	71,039	32,804
Reclassification due to determination of proved reserves		(220,491)
Capitalized exploratory well costs charged to expense	(23,375)		(29,130)
Ending balance	426,881	226,714	376,166
Aging of capitalized exploratory well costs and number of projects for which exploratory well costs were capitalized for more than one year
Exploratory well costs capitalized for a period of one year or less				$ 199,486	$ 16,814	$ 11,426
Exploratory well costs capitalized for a period one to two years				17,702	40,865	229,140
Exploratory well costs capitalized for a period three to six years				209,693	169,035	135,600
Ending balance	226,714	376,166	372,492	$ 426,881	$ 226,714	$ 376,166
Number of projects that have exploratory well costs that have been capitalized for a period greater than one year | project				3	5	8
Capitalized exploratory well costs subsequently expensed in the same period	$ 70,300	$ 1,100	$ 78,500