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Cash Equivalents and Short-term Investments Narrative (Details) | 12 Months Ended
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Jan. 31, 2020 USD ($) investment | Jan. 31, 2019 USD ($) investment | Jan. 31, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract] |  |  |
Number of short-term investments in unrealized loss positions | investment | 7 | 34 |
Gross unrealized gains or losses from available-for-sale securities | $ 0 | $ 0 | $ 0
Realized gains or losses reclassified out of accumulated other comprehensive income | 0 | 0 | $ 0
Other-than-temporary impairment short term investment | $ 0 | $ 0 |

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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455 + Details
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