Properties and Equipment, Net - Schedule of net changes in capitalized exploratory well costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net changes in capitalized exploratory well costs
Balance at beginning of period	$ 0	$ 10,557	$ 0
Additions to capitalized exploratory well costs pending the determination of proved reserves	0		10,557
Reclassifications to wells, facilities, and equipment based on the determination of proved reserves	0	(10,557)	0
Capitalized exploratory well costs charged to expense	0	0	0
Balance at end of period	$ 0	$ 0	$ 10,557