Short-Term Investments - Schedule of Fair Values and Gross Unrealized Losses of Available-for-Sale Securities Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jul. 31, 2017	Jan. 31, 2017
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	$ 24,088	$ 14,027
Gross unrealized losses	(17)	(16)
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	13,139	5,694
Gross unrealized losses	(3)	(1)
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	73,568	67,220
Gross unrealized losses	(68)	(101)
U.S. agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	79,750	40,549
Gross unrealized losses	(99)	(51)
U.S. treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	76,124	68,704
Gross unrealized losses	$ (155)	$ (111)