Fair Value Measurements (Recurring Fair Value Measurements) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets (liabilities)	$ 31,100
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	31,139	515
Liabilities	0	(5,561)
Financial assets (liabilities)	31,139	(5,046)
Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	27,784	1,978
Liabilities	0	(4,429)
Financial assets (liabilities)	27,784	(2,451)
Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	3,355	20
Liabilities	0	(2,615)
Financial assets (liabilities)	3,355	(2,595)
Commodity Contract \| Effect of Netting
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	0	(1,483)
Liabilities	0	1,483
Financial assets (liabilities)	$ 0	$ 0

Fair value, after offset of derivative liability, of 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, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, after offset of derivative asset, of 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, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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