Exploratory Costs (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) well	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) well
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Capitalized exploratory well costs at beginning of period	$ 103,588	$ 119,439	$ 119,439
Additions pending determination of proved reserves	83,446	230,061
Reclassifications due to determination of proved reserves	(81,443)	(234,291)
Capitalized exploratory well costs at end of period	105,591	$ 115,209	103,588
Capitalized Costs, Oil and Gas Producing Activities, Gross [Abstract]
Exploratory wells in progress (drilling rig not released)	2,164		1,760
Capitalized exploratory well costs capitalized for a period of one year or less	99,768		101,828
Capitalized exploratory well cost for a period greater than one year	3,659		0
Total capitalized exploratory well costs	$ 105,591		$ 103,588
Number of wells in process of drilling | well	33
Number of wells capitalized | well	1		0