Fair Value Measurements - Schedule of Financial Assets and Liabilities (Details) - USD ($)	3 Months Ended
	Apr. 30, 2022	Apr. 30, 2021	Jan. 31, 2022
Short-term investments:
Unrealized losses	$ 5,800,000
Fair value of security owned not readily marketable	7,700,000		$ 4,800,000
Payments To Acquire Non Marketable Securities	(1,119,000)	$ (936,000)
Gain on non-marketable securities	(1,751,000)	$ 0
Fair Value, Recurring
Short-term investments:
Total financial assets	1,661,413,000		1,683,240,000
Level 1 | Fair Value, Recurring
Short-term investments:
Total financial assets	1,661,413,000		1,683,240,000
Level 2 | Fair Value, Recurring
Short-term investments:
Total financial assets	0		0
Level 3 | Fair Value, Recurring
Short-term investments:
Total financial assets	0		0
U.S. government treasury securities | Fair Value, Recurring
Short-term investments:
Short-term investments:	1,372,420,000		1,352,019,000
U.S. government treasury securities | Level 1 | Fair Value, Recurring
Short-term investments:
Short-term investments:	1,372,420,000		1,352,019,000
U.S. government treasury securities | Level 2 | Fair Value, Recurring
Short-term investments:
Short-term investments:	0		0
U.S. government treasury securities | Level 3 | Fair Value, Recurring
Short-term investments:
Short-term investments:	0		0
Money market funds | Fair Value, Recurring
Cash and cash equivalents:
Cash and cash equivalents:	288,993,000		331,221,000
Money market funds | Level 1 | Fair Value, Recurring
Cash and cash equivalents:
Cash and cash equivalents:	288,993,000		331,221,000
Money market funds | Level 2 | Fair Value, Recurring
Cash and cash equivalents:
Cash and cash equivalents:	0		0
Money market funds | Level 3 | Fair Value, Recurring
Cash and cash equivalents:
Cash and cash equivalents:	$ 0		$ 0