Investments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
Apr. 30, 2020	Apr. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Realized gain (loss) on sale of marketable securities	$ 0	$ 0
Maximum
Debt Securities, Available-for-sale [Line Items]
Securities stated effective maturities (in years)	2 years

Period between issuance and maturity of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

Name:	us-gaap_DebtSecuritiesAvailableForSaleTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant