Derivative Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	$ 4,059	$ 7,896
Gross amounts netted in the consolidated balance sheet	(3,866)	(7,704)
Net amounts of assets presented in the condensed consolidated balance sheet	193	192
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	(83)	0
Counterparty A [Member] | Other Current Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	200	1,746
Gross amounts netted in the consolidated balance sheet	(200)	(1,746)
Net amounts of assets presented in the condensed consolidated balance sheet	0	0
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	0	0
Counterparty A [Member] | Other Noncurrent Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	306	0
Gross amounts netted in the consolidated balance sheet	(306)	0
Net amounts of assets presented in the condensed consolidated balance sheet	0	0
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	0	0
Counterparty B [Member] | Other Current Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	482	1,371
Gross amounts netted in the consolidated balance sheet	(482)	(1,371)
Net amounts of assets presented in the condensed consolidated balance sheet	0	0
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	0	0
Counterparty B [Member] | Other Noncurrent Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	551	841
Gross amounts netted in the consolidated balance sheet	(468)	(668)
Net amounts of assets presented in the condensed consolidated balance sheet	83	173
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	83	0
Counterparty C [Member] | Other Current Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	946	2,886
Gross amounts netted in the consolidated balance sheet	(946)	(2,873)
Net amounts of assets presented in the condensed consolidated balance sheet	0	13
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	0	0
Counterparty C [Member] | Other Noncurrent Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	889	1,046
Gross amounts netted in the consolidated balance sheet	(889)	(1,046)
Net amounts of assets presented in the condensed consolidated balance sheet	0	0
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	0	0
Counterparty D [Member] | Other Current Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	15	6
Gross amounts netted in the consolidated balance sheet	(15)	0
Net amounts of assets presented in the condensed consolidated balance sheet	0	6
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	0	0
Counterparty D [Member] | Other Noncurrent Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	0	0
Gross amounts netted in the consolidated balance sheet	0	0
Net amounts of assets presented in the condensed consolidated balance sheet	0	0
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	0	0
Counterparty E [Member] | Other Current Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	254
Gross amounts netted in the consolidated balance sheet	(232)
Net amounts of assets presented in the condensed consolidated balance sheet	22
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	0
Counterparty E [Member] | Other Noncurrent Assets [Member]
Summary of gross asset balances of derivative instruments
Gross amounts of recognized assets	416
Gross amounts netted in the consolidated balance sheet	(328)
Net amounts of assets presented in the condensed consolidated balance sheet	88
Derivative Asset, Fair Value, Subject to Master Netting, Gross Asset Basis	$ 0