Exploratory Well Costs (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capitalized Exploratory Well Costs [Abstract]
Balance at January 1		$ 2,167	$ 0	$ 8,955
Additions Pending the Determination of Proved Reserves		10,304	27,487	6,688
Reclassifications to Proved Properties		(7,917)	(20,802)	(5,274)
Costs Charged to Expense (1)	[1]	(433)	(4,518)	(10,369)
Balance at December 31		$ 4,121	$ 2,167	$ 0

[1] Includes capitalized exploratory well costs charged to either dry hole costs or impairments.