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Employee Stock Purchase Plan - Weighted Average Assumptions of Employee Stock Purchase Plan (Detail) (Employee Stock Purchase Plan [Member])
3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Employee Stock Purchase Plan [Member]
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_EmployeeStockMember
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_EmployeeStockMember
Risk-free interest rate 0.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_EmployeeStockMember
0.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_EmployeeStockMember
Volatility 30.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_EmployeeStockMember
41.30%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_EmployeeStockMember
Expected life 6 months 6 months