Impairment of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of property and equipment	$ 7,593	$ 41,917	$ 12,027
Provisions for impairment of unproved properties	2,300	2,800	15,400
Non Core Properties
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of property and equipment	5,200	37,900	$ 12,000
Drilling Rigs
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of property and equipment	$ 2,400	$ 4,000