Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative Assets
Derivative Assets, Current	$ 19,160us-gaap_DerivativeAssetsCurrent	$ 27,850us-gaap_DerivativeAssetsCurrent
Derivative Liabilities
Derivative Liabilities, Current	(473)us-gaap_DerivativeLiabilitiesCurrent	(1,249)us-gaap_DerivativeLiabilitiesCurrent
Fair Value, Net Asset (Liability)	18,687	26,601
Level 2 [Member]
Derivative Assets
Derivative Assets, Current	19,160	27,850
Derivative Liabilities
Derivative Liabilities, Current	(473)	(1,249)
Fair Value, Net Asset (Liability)	$ 18,687	$ 26,601

Fair value, after the 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, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the 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, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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