10 percent annual discount for estimated timing of cash flows.

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Summary of significant accounting policies.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

+ References

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-Name Accounting Standards Codification
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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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-Name Accounting Standards Codification
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The excess of unamortized costs capitalized within a cost center, less related deferred income taxes, over the cost center ceiling limitation, which is charged to expense for oil and gas producing companies that use full cost method of accounting for investments in oil and gas producing properties.

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-Subparagraph (SX 210.4-10(c)(4)(ii))
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Shares issuable for little or no cash consideration upon the satisfaction of certain conditions (contingently issuable shares) are considered outstanding common shares and included in the computation of basic Earnings Per Share as of the date that all necessary conditions have been satisfied (in essence, when issuance of the shares is no longer contingent). Outstanding common shares that are contingently returnable (that is, subject to recall) are treated in the same manner as contingently issuable shares. Contingently issuable shares include shares that (a) will be issued in the future upon the satisfaction of specified conditions, (b) have been placed in escrow and all or part must be returned if specified conditions are not met, or (c) have been issued but the holder must return all or part if specified conditions are not met. The number of contingently issuable shares is determined by relating the portion of time within a reporting period that these shares have been outstanding to the total time in that period.

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Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Discount rate future net revenues	10.00%
Ceiling test limitation	$ 0	$ 0
Inventory	$ 18,962,000			$ 13,450,000
Contingently issuable shares	2,800,000	0
Addition to retained earnings	$ (3,223,413,000)			$ (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	17,400,000
Crude Oil Inventory
Significant Accounting Policies [Line Items]
Inventory	$ 1,600,000