Revenue (Schedule of Information on Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Revenue [Abstract]
Sale of crude oil	$ 359,640	$ 579,030	$ 545,490
Sale of gas	34,052	49,877	55,671
Revenue	$ 393,692	$ 628,907	$ 601,161

The income arising in the course of an entity's ordinary activities. Income is increases in assets, or decreases in liabilities, that result in increases in equity, other than those relating to contributions from holders of equity claims.

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