Investments - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Jul. 31, 2021	Jan. 31, 2021
Marketable Securities [Line Items]
Amortized Cost	$ 3,173,880	$ 2,003,560
Gross Unrealized Gains	554	1,226
Gross Unrealized Losses	(405)	(376)
Estimated Fair Value	3,174,029	2,004,410
Commercial paper
Marketable Securities [Line Items]
Amortized Cost	33,729	26,222
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	33,729	26,222
Agency bonds
Marketable Securities [Line Items]
Amortized Cost	491,968	461,335
Gross Unrealized Gains	82	79
Gross Unrealized Losses	(53)	(49)
Estimated Fair Value	491,997	461,365
Corporate and other debt securities
Marketable Securities [Line Items]
Amortized Cost	380,373	465,207
Gross Unrealized Gains	314	1,113
Gross Unrealized Losses	(89)	(64)
Estimated Fair Value	380,598	466,256
U.S. government agency securities
Marketable Securities [Line Items]
Amortized Cost	2,213,814	834,894
Gross Unrealized Gains	157	28
Gross Unrealized Losses	(259)	(257)
Estimated Fair Value	2,213,712	834,665
Treasury bills
Marketable Securities [Line Items]
Amortized Cost	53,996	215,902
Gross Unrealized Gains	1	6
Gross Unrealized Losses	(4)	(6)
Estimated Fair Value	$ 53,993	$ 215,902