Fair Value Measurements - Warrant Derivative Liability (Narrative) (Details)  | 
 Apr. 30, 2018  
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| Warrants With Price Protection [Member] | Ìý | 
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | Ìý | 
| Number of warrants containing price protection | 62,500 | 
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- Definition Number of warrants or rights outstanding. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Details 
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