Suspended Well Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) project	Dec. 31, 2017 USD ($) project	Dec. 31, 2016 USD ($) project
Reconciliation of capitalized exploratory well costs on completed wells
Beginning balance	$ 410,113	$ 734,463	$ 426,881
Additions to capitalized exploratory well costs pending the determination of proved reserves	10,518	69,567	307,582
Additions associated with the acquisition of DGE	26,224	0	0
Reclassification due to determination of proved reserves	(26,224)	(176,881)	0
Divestitures	0	(206,400)	0
Contribution of oil and gas property to equity method investment - KBSL	0	(131,764)	0
Dissolution of equity method investment - KBSL	0	121,128	0
Capitalized exploratory well costs charged to expense	(52,966)	0	0
Ending balance	367,665	410,113	734,463
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				$ 0	$ 67,159	$ 279,809
Exploratory well costs capitalized for a period of one to two years				299,253	291,252	244,804
Exploratory well costs capitalized for a period of three years or longer				68,412	51,702	209,850
Ending balance	410,113	$ 734,463	$ 426,881	$ 367,665	$ 410,113	$ 734,463
Number of projects that have exploratory well costs that have been capitalized for a period greater than one year | project				3	5	5
Akasa Discovery
Reconciliation of capitalized exploratory well costs on completed wells
Capitalized exploratory well costs charged to expense	(38,100)
Wawa Discovery
Reconciliation of capitalized exploratory well costs on completed wells
Capitalized exploratory well costs charged to expense	$ (13,600)