Fair Value Measurements (Details) - USD ($) $ in Thousands	Oct. 31, 2020	Jan. 31, 2020
Assets, Fair Value Disclosure
Cash equivalents:	$ 3,832,634	$ 54,297
Short-term investments	814,123	306,844
Long-term investments	347,403	23,532
Total	4,994,160	384,673
U.S. government and agency securities
Assets, Fair Value Disclosure
Cash equivalents:	3,778,212	32,472
Money market funds
Assets, Fair Value Disclosure
Cash equivalents:	54,422	21,379
Commercial paper
Assets, Fair Value Disclosure
Cash equivalents:		446
Level 1
Assets, Fair Value Disclosure
Total	54,422	21,379
Level 2
Assets, Fair Value Disclosure
Total	4,939,738	363,294
Recurring | U.S. government and agency securities
Assets, Fair Value Disclosure
Short-term investments	681,018	245,756
Long-term investments	301,978	14,197
Recurring | Corporate notes and bonds
Assets, Fair Value Disclosure
Short-term investments	66,946	23,674
Long-term investments	45,178	7,025
Recurring | Certificates of deposit
Assets, Fair Value Disclosure
Short-term investments	45,312	10,899
Long-term investments		1,705
Recurring | Commercial paper
Assets, Fair Value Disclosure
Short-term investments	20,847	17,008
Recurring | Asset-backed securities
Assets, Fair Value Disclosure
Short-term investments		9,507
Long-term investments	247	605
Recurring | U.S. government and agency securities
Assets, Fair Value Disclosure
Cash equivalents:	3,778,212	32,472
Recurring | Money market funds
Assets, Fair Value Disclosure
Cash equivalents:	54,422	21,379
Recurring | Commercial paper
Assets, Fair Value Disclosure
Cash equivalents:		446
Recurring | Level 1 | U.S. government and agency securities
Assets, Fair Value Disclosure
Short-term investments	0	0
Long-term investments	0	0
Recurring | Level 1 | Corporate notes and bonds
Assets, Fair Value Disclosure
Short-term investments	0	0
Long-term investments	0	0
Recurring | Level 1 | Certificates of deposit
Assets, Fair Value Disclosure
Short-term investments	0	0
Long-term investments		0
Recurring | Level 1 | Commercial paper
Assets, Fair Value Disclosure
Short-term investments	0	0
Recurring | Level 1 | Asset-backed securities
Assets, Fair Value Disclosure
Short-term investments		0
Long-term investments	0	0
Recurring | Level 1 | U.S. government and agency securities
Assets, Fair Value Disclosure
Cash equivalents:	0	0
Recurring | Level 1 | Money market funds
Assets, Fair Value Disclosure
Cash equivalents:	54,422	21,379
Recurring | Level 1 | Commercial paper
Assets, Fair Value Disclosure
Cash equivalents:		0
Recurring | Level 2 | U.S. government and agency securities
Assets, Fair Value Disclosure
Short-term investments	681,018	245,756
Long-term investments	301,978	14,197
Recurring | Level 2 | Corporate notes and bonds
Assets, Fair Value Disclosure
Short-term investments	66,946	23,674
Long-term investments	45,178	7,025
Recurring | Level 2 | Certificates of deposit
Assets, Fair Value Disclosure
Short-term investments	45,312	10,899
Long-term investments		1,705
Recurring | Level 2 | Commercial paper
Assets, Fair Value Disclosure
Short-term investments	20,847	17,008
Recurring | Level 2 | Asset-backed securities
Assets, Fair Value Disclosure
Short-term investments		9,507
Long-term investments	247	605
Recurring | Level 2 | U.S. government and agency securities
Assets, Fair Value Disclosure
Cash equivalents:	3,778,212	32,472
Recurring | Level 2 | Money market funds
Assets, Fair Value Disclosure
Cash equivalents:	$ 0	0
Recurring | Level 2 | Commercial paper
Assets, Fair Value Disclosure
Cash equivalents:		$ 446