Fair Value Measurements - Inputs (Details)	6 Months Ended	12 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Fair Value Disclosures [Abstract]
Rate reflecting our nonperformance risk	1.75%	1.75%
Weighted-average rate reflecting our counterparties' nonperformance risk	1.56%	3.38%

Risk associated with risk of default, credit spread risk and downgrade risk, expressed as a percentage, used as an input to measure fair value.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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