Member Power Bill Prepayments (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Member Power Bill Prepayments
Member power bill prepayments	$ 114,546,000
Member power bill prepayments classified as current liability	65,573,000	66,819,000
Member power bill prepayments classified as deferred credits and other liabilities	$ 48,973,000	$ 35,500,000