Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Jan. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 211,395	$ 210,313
Unrealized Gains	1,022	770
Unrealized Losses	(617)	(2)
Fair Value	211,800	211,081
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,011	8,284
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	2,011	8,284
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,902	63,390
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	61,902	63,390
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	103,681	95,053
Unrealized Gains	726	653
Unrealized Losses	(599)
Fair Value	103,808	95,706
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,742	23,062
Unrealized Gains	152	69
Unrealized Losses	(18)	(2)
Fair Value	23,876	23,129
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,059	20,524
Unrealized Gains	144	48
Fair Value	$ 20,203	$ 20,572

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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