Exploratory Costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 well	Mar. 31, 2013
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Capitalized exploratory well costs at beginning of period	$ 57,600	$ 79,791
Additions pending determination of proved reserves	164,842	95,861
Reclassifications due to determination of proved reserves	(112,474)	(69,477)
Capitalized exploratory well costs at end of period	109,968	106,175
Exploratory wells in progress	62,280	21,676
Capitalized exploratory well costs capitalized for a period of one year or less	46,460	83,301
Capitalized exploratory well costs for a period greater than one year	1,228	1,198
Total capitalized exploratory well costs	$ 109,968	$ 106,175
Wells in process of drilling	45
Wells capitalized greater than one year pending results from completion and testing	1