Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) - Commodity Contract - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	$ 700,000
Transfers into Level 3	0	$ 0
Transfers out of Level 3	$ 0	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

Amount of gain (loss) recognized in the income statement of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19279-110258

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- Definition

Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into level 3 of the fair value hierarchy.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19279-110258

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- Definition

Amount of transfers of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset) out of level 3 of the fair value hierarchy.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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-Section 50
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-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19279-110258

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