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Regulatory Liabilities (Detail) (USD $) In Millions, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012 | Sep. 30, 2012
--- | --- | --- | ---
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities | $ 11.4 | $ 6.8 | $ 7.3
Regulatory Tracker Mechanisms |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities | $ 11.4 | $ 6.8 | $ 7.3

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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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