Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets and liabilities subject to fair value measurements
Outstanding Balance	$ 2,600,000	$ 2,600,000
Commodity contract \| Futures
Assets and liabilities subject to fair value measurements
Commodity futures - financial assets	1,642	1,765
Commodity futures - financial liabilities	3,177	3,925
Recurring \| Total \| Commodity contract \| Futures
Assets and liabilities subject to fair value measurements
Commodity futures - financial assets	1,642	1,765
Commodity futures - financial liabilities	3,177	3,925
Recurring \| Level 2
Assets and liabilities subject to fair value measurements
Fair value of long-term debt, including current maturities	2,600,000	2,500,000
Recurring \| Level 2 \| Commodity contract \| Futures
Assets and liabilities subject to fair value measurements
Commodity futures - financial assets	1,642	1,765
Commodity futures - financial liabilities	$ 3,177	$ 3,925

Fair value, before effects of master netting arrangements, of a financial asset or other 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 assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 3
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
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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.

+ References

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)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Publisher SEC
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-Paragraph 20, 22
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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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