Properties and Equipment, Net - Schedule of net changes in capitalized exploratory well costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net changes in capitalized exploratory well costs
Balance at beginning of period	$ 10,557	$ 0	$ 10,390
Additions to capitalized exploratory well costs pending the determination of proved reserves	0	10,557	0
Reclassifications to wells, facilities, and equipment based on the determination of proved reserves	(10,557)	0	(10,198)
Capitalized exploratory well costs charged to expense	0	0	(192)
Balance at end of period	$ 0	$ 10,557	$ 0