Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Jan. 31, 2020	Jan. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 210,313	$ 205,009
Unrealized Gains	770	176
Unrealized Losses	(2)	(79)
Fair Value	211,081	205,106
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,284	8,914
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	8,284	8,914
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		7,012
Unrealized Gains		0
Unrealized Losses		0
Fair Value		7,012
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	63,390	68,233
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	63,390	68,233
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	95,053	87,250
Unrealized Gains	653	170
Unrealized Losses	0	(60)
Fair Value	95,706	87,360
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,062	11,607
Unrealized Gains	69	3
Unrealized Losses	(2)	(6)
Fair Value	23,129	11,604
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,524	21,993
Unrealized Gains	48	3
Unrealized Losses	0	(13)
Fair Value	$ 20,572	$ 21,983

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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