Suspended Well Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net changes in capitalized exploratory well costs
Beginning balance	$ 11,925	$ 11,197	$ 49,446
Additions to capitalized exploratory well costs pending the determination of proved reserves	3,346	11,925	11,197
Divestitures	0	0	(109)
Reclassifications based on the determination of proved reserves	(9,573)	(11,197)	(49,337)
Capitalized exploratory well costs charged to expense	0	0	0
Ending balance	5,698	$ 11,925	$ 11,197
Exploratory well costs capitalized for more than one year	$ 0