Cash Equivalents and Short-term Investments - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2020 USD ($) investment	Oct. 31, 2019 USD ($)	Oct. 31, 2020 USD ($) investment	Oct. 31, 2019 USD ($)	Jan. 31, 2020 USD ($) investment
Investments, Debt and Equity Securities [Abstract]
Short-term Investments	$ 41,000,000.0		$ 41,000,000.0		$ 0
Interest receivable	$ 10,900,000		$ 10,900,000		$ 5,700,000
Number of short-term investments in unrealized loss positions (in investments) | investment	62		62		7
Gross unrealized gains or losses from available-for-sale securities	$ 0	$ 0	$ 0	$ 0
Realized gains or losses reclassified out of accumulated other comprehensive income	$ 0	$ 0	0	$ 0
Other-than-temporary impairment short term investment			$ 0		$ 0