Short-Term Investments - Schedule of Fair Values and Gross Unrealized Losses of Available-for-Sale Securities Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Oct. 31, 2016	Jan. 31, 2016
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 12,108	$ 2,249
Gross Unrealized Losses	(6)	(2)
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	10,517
Gross Unrealized Losses	(10)
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	60,122	14,296
Gross Unrealized Losses	(73)	(40)
U.S. agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	20,493	82,806
Gross Unrealized Losses	(15)	(54)
U.S. treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	61,156	33,486
Gross Unrealized Losses	$ (44)	$ (37)