Exploratory Costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014 well	Sep. 30, 2013	Sep. 30, 2014 well	Sep. 30, 2013	Dec. 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	$ 166,458	$ 72,172	$ 57,600	$ 79,791
Additions pending determination of proved reserves	258,724	99,428	623,913	319,008
Reclassifications due to determination of proved reserves	(258,123)	(112,821)	(513,263)	(340,020)
Exploratory well costs charged to expense	(1,217)	0	(2,408)	0
Capitalized exploratory well costs at end of period	165,842	58,779	165,842	58,779
Exploratory wells in progress	29,059		29,059		14,794
Capitalized exploratory well costs capitalized for a period of one year or less	136,783		136,783		42,481
Capitalized exploratory well costs for a period greater than one year	0		0		1,206
Total capitalized exploratory well costs	$ 165,842		$ 165,842		$ 58,481
Number of wells in process of drilling	56		56