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Summary of Significant Accounting Policies - Schedule of Regulatory Assets and Liabilities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2012
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FPU [Member] |
Schedule Of Regulatory Assets And Liabilities [Line Items] |
Premium paid by FPU for acquisition | $ 1.3
Parent [Member] |
Schedule Of Regulatory Assets And Liabilities [Line Items] |
Premium paid for acquisition | $ 34.2

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