Commitments and Contingencies - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jul. 31, 2019	Jan. 31, 2019
Loss Contingencies [Line Items]
Total manufacturing purchase commitments	$ 41,300,000	$ 28,200,000
Indemnification agreement [Member]
Loss Contingencies [Line Items]
Payments under indemnification obligations	0	0
Liabilities recorded under indemnification obligations	$ 0	$ 0