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Financial Instruments (Narrative) (Details) - USD ($) | 3 Months Ended |
--- | --- | ---
Apr. 30, 2020 | Apr. 30, 2019 | Jan. 31, 2020
Investments, All Other Investments [Abstract] |  |  |
Securities in a continuous unrealized loss position for more than 12 months | $ 0 |  | $ 0
Allowance for credit loss | 0 |  |
Securities, writeoff | 0 |  |
Gain (loss) from sale or redemption of available for sale securities | 0 | $ 0 |
Proceeds from sale and maturity of marketable securities | 0 | $ 4,600,000 |
Direct investments in privately held companies | $ 148,500,000 |  | $ 122,500,000

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- Definition Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aaa) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454 + Details
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