Exploratory Well Costs (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Capitalized Exploratory Well Costs [Abstract]
Balance at January 1	$ 9,211,000		$ 49,116,000	[1]	$ 61,111,000
Additions Pending the Determination of Proved Reserves	32,080,000		52,099,000		73,332,000
Reclassifications to Proved Properties	(15,946,000)		(54,505,000)		(69,462,000)
Costs Charged to Expense (1)	(8,092,000)	[2]	(35,859,000)	[2]	(17,115,000)	[2]
Foreign Currency Translations	0		(1,640,000)		1,250,000
Balance at December 31	17,253,000		9,211,000		49,116,000	[1]
Exploratory well costs related to an outside operated, offshore Central North Sea project in the United Kingdom					$ 21,000,000

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjI5ZmZlZTBlYzU1OTQ1ZWU4NGU2MjcxZTg5NmM2NzFifFRleHRTZWxlY3Rpb246RUVDMkRDOTE5REM5MDc0REVCQzZBNjNEQjU1QTFCMjIM}

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