| Fair Value Measurements - Warrant Derivative Liability (Narrative) (Details) | Apr. 30, 2018  shares | 
|---|---|
| Warrants With Price Protection [Member] | 听 | 
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | 听 | 
| Number of warrants containing price protection | 62,500 | 
| X | ||||||||||
| 
- Definition Number of warrants or rights outstanding. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- 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. 
 | 
| X | ||||||||||
| 
- Details 
 |