Short-Term Investments - Schedule of Short-Term Investments (Detail) - USD ($) $ in Thousands	Oct. 31, 2020	Jan. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 952,039	$ 607,454
Gross unrealized gains	4,344	2,565
Gross unrealized losses	(216)	(4)
Estimated fair value	956,167	610,015
Certificates of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	15,600	3,500
Gross unrealized gains	13	3
Gross unrealized losses	(1)	0
Estimated fair value	15,612	3,503
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	130,733	100,419
Gross unrealized gains	821	396
Gross unrealized losses	(10)	(1)
Estimated fair value	131,544	100,814
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	58,602	19,965
Gross unrealized gains	35	5
Gross unrealized losses	(1)	(1)
Estimated fair value	58,636	19,969
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	414,837	234,664
Gross unrealized gains	2,528	1,552
Gross unrealized losses	(184)	(2)
Estimated fair value	417,181	236,214
Foreign government bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	32,011	3,397
Gross unrealized gains	33	10
Gross unrealized losses	(17)	0
Estimated fair value	32,027	3,407
U.S. agency obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	52,751
Gross unrealized gains	71
Gross unrealized losses	0
Estimated fair value	52,822
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	247,505	245,509
Gross unrealized gains	843	599
Gross unrealized losses	(3)	0
Estimated fair value	$ 248,345	$ 246,108