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Significant Accounting Policies - Additional Information (Details) - USD ($) shares in Millions	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2015	Jan. 01, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Discount rate future net revenues				10.00%
Ceiling test limitation		$ 0	$ 0
Inventory	$ 20,202,000	$ 20,202,000				$ 13,450,000
Contingently issuable shares	4.9	2.5
Addition to retained earnings	$ (3,225,405,000)	$ (3,225,405,000)				$ (3,270,605,000)
Accounting Standards Update 2014-09 \| Difference between Revenue Guidance in Effect before and after Topic 606
Significant Accounting Policies [Line Items]
Addition to retained earnings					$ 1,800,000
Pipe and Production Equipment
Significant Accounting Policies [Line Items]
Inventory	19,000,000	19,000,000
Crude Oil Inventory
Significant Accounting Policies [Line Items]
Inventory	$ 1,200,000	$ 1,200,000
Reserve Fund for Interest Claims
Significant Accounting Policies [Line Items]
Restricted cash			$ 400,000,000