Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Jul. 31, 2019	Jan. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 207,784	$ 205,009
Unrealized Gains	569	176
Unrealized Losses	(24)	(79)
Fair Value	208,329	205,106
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,409	8,914
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	17,409	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	59,934	68,233
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	59,934	68,233
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	96,237	87,250
Unrealized Gains	525	170
Unrealized Losses	(4)	(60)
Fair Value	96,758	87,360
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,460	11,607
Unrealized Gains	42	3
Unrealized Losses	(2)	(6)
Fair Value	14,500	11,604
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,744	21,993
Unrealized Gains	2	3
Unrealized Losses	(18)	(13)
Fair Value	$ 19,728	$ 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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