Derivatives (Details Textuals) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Derivative [Line Items]
Maximum counterparty loss	$ 3.4
Maximum counterparty loss with netting feature	3.1
Cash Flow Liquid Swap [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax	1.1
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	$ 1.0

Amount of unrealized gain (loss) arising from the change in fair value of price risk derivatives designated as cash flow hedging instruments recorded in accumulated other comprehensive income in the period, before taxes, to the extent that the cash flow hedge is determined to be effective.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 30, 46

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_UnrealizedGainLossOnPriceRiskCashFlowDerivativesBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration