Fair Value Measurements (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010
Fair Value Measurements [Abstract]
Percent of derivatives expiring	99.00%
Tenure of expiry of derivatives portfolio (months)	15 months
Fair Value, Level 1 to level 2 Transfers, Amount	$ 0	$ 0
Fair Value, Level 2 to level 1 Transfers, Amount	$ 0	$ 0

The amount of the transfers of assets or liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

Name:	us-gaap_FairValueLevel1ToLevel2TransfersAmount
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration