Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	Jan. 31, 2018
Loss Contingencies [Line Items]
Net operating lease expense	$ 1,100,000	$ 1,200,000	$ 2,300,000	$ 2,900,000
Total manufacturing purchase commitments	22,100,000		22,100,000		$ 24,300,000
Indemnification agreement [Member]
Loss Contingencies [Line Items]
Payments under indemnification obligations			0		0
Liabilities recorded under indemnification obligations	$ 0		$ 0		$ 0