Commodity Derivative Contracts (Details Textuals)	6 Months Ended
Jun. 30, 2015
Minimum
Derivative [Line Items]
Derivative, Average Remaining Maturity	18 months
Maximum
Derivative [Line Items]
Derivative, Average Remaining Maturity	2 years

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_DerivativeAverageRemainingMaturity1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration