Derivative Instruments and Concentration of Credit Risk (Details Textual)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments and Concentration of Credit Risk (Textuals) [Abstract]
Customer accounted for ten percent of consolidated revenues	1	1	1
Consolidated revenue, major customer, percentage	14.00%	17.00%	15.00%

Percentage of revenue generated from a single external customer that accounts for 10 percent or more of an entity's revenues.

No definition available.

Name:	us-gaap_EntityWideRevenueMajorCustomerPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration