Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Apr. 30, 2017	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 101,146	$ 100,920
Unrealized Gains	7	13
Unrealized Losses	(95)	(83)
Fair Value	101,058	100,850
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	74	8,328
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	74	8,328
Demand deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,000	10,000
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	15,000	10,000
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,762	4,784
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	10,762	4,784
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	41,281	42,713
Unrealized Gains	6	6
Unrealized Losses	(32)	(41)
Fair Value	41,255	42,678
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,621	11,686
Unrealized Gains	1	1
Unrealized Losses	(10)	(12)
Fair Value	10,612	11,675
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,408	23,409
Unrealized Gains	0	6
Unrealized Losses	(53)	(30)
Fair Value	$ 23,355	$ 23,385