Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=SL51823488-111719

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

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Financial Instruments and Risk Management (Fair Value of Derivative Instruments Not Designated as Hedging Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Commodity Derivative Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 18,300		$ 1,700
Foreign Exchange Derivative Contracts [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives			$ (100)
Nondesignated [Member] \| Commodity Derivative Contracts [Member] \| Accounts Receivable [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 18,297
Nondesignated [Member] \| Commodity Derivative Contracts [Member] \| Accounts Payable [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives		$ (48,864)
Nondesignated [Member] \| Foreign Exchange Derivative Contracts [Member] \| Accounts Payable [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives		$ (73)