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Presentation and Summary of Significant Accounting Policies - Revenue recognition timing (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-05-01
Apr. 30, 2019
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]  
Revenue recognition of remaining performance obligations 75.00%
Revenue recognition in next twelve months 12 months