Property, Plant And Equipment - Net Changes in Capitalized Exploratory Well Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Beginning balance at January 1	$ 217,326	$ 207,855	$ 155,103
Additions pending the determination of proved reserves	3,999	83,712	59,487
Reclassifications to proved properties based on the determination of proved reserves	0	(61,096)	(2,214)
Capitalized exploration well costs charged to expense	(39,709)	(13,145)	(4,521)
Ending balance at December 31	$ 181,616	$ 217,326	$ 207,855