Exploratory Well Costs (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Capitalized Exploratory Well Costs [Abstract]
Balance at January 1		$ 8,955	$ 17,253	$ 9,211
Additions Pending the Determination of Proved Reserves		6,688	24,640	32,080
Reclassifications to Proved Properties		(5,274)	(26,659)	(15,946)
Costs Charged to Expense (1)	[1]	(10,369)	(6,279)	(8,092)
Balance at December 31		$ 0	$ 8,955	$ 17,253

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