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Critical Accounting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Jun. 30, 2013
Sep. 30, 2013
Regulatory Assets [Abstract]    
Valuation allowance $ 5.9  
Statutory tax rate   34.00%
Possible income tax charge due to tax examination   $ 1.57