Exploratory Costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014 well	Jun. 30, 2013	Jun. 30, 2014 well	Jun. 30, 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	$ 109,968	$ 106,175	$ 57,600	$ 79,791
Additions pending determination of proved reserves	200,347	123,719	365,189	219,580
Reclassifications due to determination of proved reserves	(142,666)	(157,722)	(255,140)	(227,199)
Exploratory well costs charged to expense	(1,191)	0	(1,191)	0
Capitalized exploratory well costs at end of period	166,458	72,172	166,458	72,172
Exploratory wells in progress	35,753	25,728	35,753	25,728
Capitalized exploratory well costs capitalized for a period of one year or less	129,477	45,245	129,477	45,245
Capitalized exploratory well costs for a period greater than one year	1,228	1,199	1,228	1,199
Total capitalized exploratory well costs	$ 166,458	$ 72,172	$ 166,458	$ 72,172
Number of wells in process of drilling	56		56
Number of gross well capitalized greater than a year which is pending results from completion and testing	1		1