Short-Term Investments - Schedule of Short-Term Investments (Detail) - USD ($) $ in Thousands	Jan. 31, 2020	Jan. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	$ 607,454	$ 539,743
Available-for-sale securities, Gross unrealized gains	2,565	282
Available-for-sale securities, Gross unrealized losses	(4)	(835)
Available-for-sale securities, Estimated fair value	610,015	539,190
Certificates of deposits
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	3,500	6,001
Available-for-sale securities, Gross unrealized gains	3	10
Available-for-sale securities, Gross unrealized losses	0	(1)
Available-for-sale securities, Estimated fair value	3,503	6,010
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	100,419	78,682
Available-for-sale securities, Gross unrealized gains	396	13
Available-for-sale securities, Gross unrealized losses	(1)	(300)
Available-for-sale securities, Estimated fair value	100,814	78,395
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	19,965	9,118
Available-for-sale securities, Gross unrealized gains	5	1
Available-for-sale securities, Gross unrealized losses	(1)	(2)
Available-for-sale securities, Estimated fair value	19,969	9,117
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	234,664	185,409
Available-for-sale securities, Gross unrealized gains	1,552	178
Available-for-sale securities, Gross unrealized losses	(2)	(457)
Available-for-sale securities, Estimated fair value	236,214	185,130
Foreign government bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	3,397	1,502
Available-for-sale securities, Gross unrealized gains	10	0
Available-for-sale securities, Gross unrealized losses	0	(11)
Available-for-sale securities, Estimated fair value	3,407	1,491
U.S. agency obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		15,912
Available-for-sale securities, Gross unrealized gains		2
Available-for-sale securities, Gross unrealized losses		(2)
Available-for-sale securities, Estimated fair value		15,912
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	245,509	243,119
Available-for-sale securities, Gross unrealized gains	599	78
Available-for-sale securities, Gross unrealized losses	0	(62)
Available-for-sale securities, Estimated fair value	$ 246,108	$ 243,135

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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-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
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