Cash Equivalents and Short-term Investments - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
Apr. 30, 2020 USD ($) investment	Apr. 30, 2019 USD ($)	Jan. 31, 2020 USD ($) investment
Investments, Debt and Equity Securities [Abstract]
Number of short-term investments in unrealized loss positions (in investments) \| investment	12		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		$ 0.0

Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI).

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