Commitments and Contingencies (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Write off of Amortization of Leased Assets [Line Items]
Non-cash provision for leased items no longer in use	$ 0		$ 0	$ 12,589	$ 0
Onshore Facilities & Transportation
Write off of Amortization of Leased Assets [Line Items]
Non-cash provision for leased items no longer in use		$ 12,600
Accrued Liabilities
Write off of Amortization of Leased Assets [Line Items]
Loss contingency, accrual, current	$ 4,100			$ 4,100