Short-Term Investments - Schedule of Short-Term Investments (Detail) - USD ($) $ in Thousands	Apr. 30, 2020	Jan. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 655,926	$ 607,454
Gross unrealized gains	4,959	2,565
Gross unrealized losses	(686)	(4)
Estimated fair value	660,199	610,015
Certificates of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	11,600	3,500
Gross unrealized gains	38	3
Gross unrealized losses	(55)	0
Estimated fair value	11,583	3,503
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	104,406	100,419
Gross unrealized gains	476	396
Gross unrealized losses	(162)	(1)
Estimated fair value	104,720	100,814
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	37,028	19,965
Gross unrealized gains	47	5
Gross unrealized losses	(24)	(1)
Estimated fair value	37,051	19,969
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	270,889	234,664
Gross unrealized gains	2,283	1,552
Gross unrealized losses	(410)	(2)
Estimated fair value	272,762	236,214
Foreign government bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	4,803	3,397
Gross unrealized gains	32	10
Gross unrealized losses	(35)	0
Estimated fair value	4,800	3,407
U.S. agency obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	4,999
Gross unrealized gains	3
Gross unrealized losses	0
Estimated fair value	5,002
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	222,201	245,509
Gross unrealized gains	2,080	599
Gross unrealized losses	0	0
Estimated fair value	$ 224,281	$ 246,108