Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015 Impaired_Asset_And_Liability	Mar. 31, 2014 Impaired_Asset_And_Liability	Dec. 31, 2014
Assets
Deferred compensation plan	$ 13,322us-gaap_DeferredCompensationPlanAssets		$ 13,115us-gaap_DeferredCompensationPlanAssets
Derivative contracts	134,041		137,603
Total assets	147,363us-gaap_AssetsFairValueDisclosure		150,718us-gaap_AssetsFairValueDisclosure
Liabilities
Deferred compensation plan	29,096		28,932
Total liabilities	29,096us-gaap_LiabilitiesFairValueDisclosure		28,932us-gaap_LiabilitiesFairValueDisclosure
Number of non-financial assets and liabilities impaired	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Recurring basis
Assets
Deferred compensation plan	13,322		13,115
Derivative contracts	0		0
Total assets	13,322		13,115
Liabilities
Deferred compensation plan	29,096		28,932
Total liabilities	29,096		28,932
Significant Other Observable Inputs (Level 2) \| Recurring basis
Assets
Deferred compensation plan	0		0
Derivative contracts	50,716		51,645
Total assets	50,716		51,645
Liabilities
Deferred compensation plan	0		0
Total liabilities	0		0
Significant Unobservable Inputs (Level 3) \| Recurring basis
Assets
Deferred compensation plan	0		0
Derivative contracts	83,325		85,958
Total assets	83,325		85,958
Liabilities
Deferred compensation plan	0		0
Total liabilities	$ 0		$ 0

Represents the number of non-financial assets and liabilities that were impaired during the period.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements payable beyond one year (or the operating cycle, if longer).

+ References

No definition available.

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- Definition

Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 17

-Article 5

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- Definition

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.

+ References

Reference 1: 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=34720828&loc=SL20225862-175312

Reference 2: 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=35706170&loc=SL5624163-113959

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226000-175313

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

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