Short-Term Investments - Schedule of Fair Values and Gross Unrealized Loss Position of Available-for-Sale Securities Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Apr. 30, 2019	Jan. 31, 2019
Certificates of deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value		$ 999
Gross unrealized losses		(1)
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	$ 40,460	69,131
Gross unrealized losses	(138)	(300)
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	2,973	7,155
Gross unrealized losses		(2)
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	53,533	121,006
Gross unrealized losses	(206)	(457)
Foreign government bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	1,494	1,490
Gross unrealized losses	(8)	(11)
U.S. treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value	85,774	130,785
Gross unrealized losses	$ (8)	(62)
U.S. agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value		14,928
Gross unrealized losses		$ (2)