Divestitures (Details)	1 Months Ended
Jun. 30, 2011 Constellation Energy Partners LLC	Dec. 31, 2010 Quail Run Energy Center MW
Definitive purchase and sale agreement
Number of members on board to be appointed on account of divestiture rights sold	2
Total number of members on board	5
Underlying power generation capacity of acquired entities (in megawatts)		550

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