Properties and Equipment, Net - Schedule of aging of capitalized exploratory well costs (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Capitalized exploratory well costs
Capitalized exploratory well costs that have been capitalized for a period of one year or less	$ 0	$ 10,557	$ 0
Capitalized exploratory well costs that have been capitalized for a period greater than one year	0	0	0
Capitalized Exploratory Well Costs	$ 0	$ 10,557	$ 0	$ 10,390