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Investments - Additional Information (Detail) (USD $)
3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]    
Other-than-temporary impairment charges recognized $ 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet $ 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet