Investments - Summary Marketable Securities (Details) - USD ($) $ in Thousands	Jan. 31, 2022	Jan. 31, 2021
Marketable Securities [Line Items]
Amortized Cost	$ 4,380,350	$ 2,003,560
Gross Unrealized Gains	35	1,226
Gross Unrealized Losses	(23,939)	(376)
Estimated Fair Value	4,356,446	2,004,410
Commercial paper
Marketable Securities [Line Items]
Amortized Cost	28,723	26,222
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	28,723	26,222
Agency bonds
Marketable Securities [Line Items]
Amortized Cost	632,935	461,335
Gross Unrealized Gains	2	79
Gross Unrealized Losses	(3,328)	(49)
Estimated Fair Value	629,609	461,365
Corporate and other debt securities
Marketable Securities [Line Items]
Amortized Cost	282,124	465,207
Gross Unrealized Gains	5	1,113
Gross Unrealized Losses	(1,202)	(64)
Estimated Fair Value	280,927	466,256
U.S. government agency securities
Marketable Securities [Line Items]
Amortized Cost	3,046,742	834,894
Gross Unrealized Gains	28	28
Gross Unrealized Losses	(19,261)	(257)
Estimated Fair Value	3,027,509	834,665
Treasury bills
Marketable Securities [Line Items]
Amortized Cost	389,826	215,902
Gross Unrealized Gains	0	6
Gross Unrealized Losses	(148)	(6)
Estimated Fair Value	$ 389,678	$ 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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