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Commitments and Contingencies - Additional Information (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Apr. 30, 2018
Apr. 30, 2017
Jan. 31, 2018
Loss Contingencies [Line Items]      
Net operating lease expense $ 1,200,000 $ 1,700,000  
Total manufacturing purchase commitments 32,100,000   $ 24,300,000
Indemnification agreement [Member]      
Loss Contingencies [Line Items]      
Payments under indemnification obligations 0   0
Liabilities recorded under indemnification obligations $ 0   $ 0