Marketable Securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Apr. 30, 2021	Jan. 31, 2021
Marketable Securities [Line Items]
Amortized Cost	$ 3,132,112	$ 2,003,560
Gross Unrealized Gains	744	1,226
Gross Unrealized Losses	(547)	(376)
Estimated Fair Value	3,132,309	2,004,410
Commercial paper
Marketable Securities [Line Items]
Amortized Cost	57,707	26,222
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	57,707	26,222
Agency bonds
Marketable Securities [Line Items]
Amortized Cost	515,261	461,335
Gross Unrealized Gains	44	79
Gross Unrealized Losses	(148)	(49)
Estimated Fair Value	515,157	461,365
Corporate and other debt securities
Marketable Securities [Line Items]
Amortized Cost	469,972	465,207
Gross Unrealized Gains	563	1,113
Gross Unrealized Losses	(107)	(64)
Estimated Fair Value	470,428	466,256
U.S. government agency securities
Marketable Securities [Line Items]
Amortized Cost	1,876,688	834,894
Gross Unrealized Gains	124	28
Gross Unrealized Losses	(292)	(257)
Estimated Fair Value	1,876,520	834,665
Treasury bills
Marketable Securities [Line Items]
Amortized Cost	212,484	215,902
Gross Unrealized Gains	13	6
Gross Unrealized Losses	0	(6)
Estimated Fair Value	$ 212,497	$ 215,902

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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