Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016	Jan. 31, 2017
Loss Contingencies [Line Items]
Net operating lease expense	$ 1,200,000	$ 1,900,000	$ 2,900,000	$ 3,600,000
Total manufacturing purchase commitments	36,800,000		36,800,000		$ 23,900,000
Indemnification agreement [Member]
Loss Contingencies [Line Items]
Payments under indemnification obligations			0		0
Liabilities recorded under indemnification obligations	$ 0		$ 0		$ 0