Exploratory Costs (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) well	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) well	Sep. 30, 2015 USD ($)	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	$ 37,438	$ 99,926	$ 103,588	$ 119,439	$ 119,439
Additions pending determination of proved reserves	88,879	113,734	250,782	533,255
Reclassifications due to determination of proved reserves	(44,564)	(82,325)	(272,617)	(521,359)
Capitalized exploratory well costs at end of period	81,753	$ 131,335	81,753	$ 131,335	103,588
Capitalized Costs, Oil and Gas Producing Activities, Gross [Abstract]
Exploratory wells in progress (drilling rig not released)	33,818		33,818		1,760
Capitalized exploratory well costs capitalized for a period of one year or less	41,048		41,048		101,828
Capitalized exploratory well cost for a period greater than one year	6,887		6,887		0
Total capitalized exploratory well costs	$ 81,753		$ 81,753		$ 103,588
Number of wells in process of drilling | well	46		46
Number of wells capitalized | well			2		0