| Stockholders' Equity - Warrants (Details) | 3 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Jun. 05, 2020  $ / shares | Apr. 30, 2020  shares | Aug. 20, 2019  investor  shares | Aug. 17, 2019  shares | Mar. 06, 2019  $ / shares | Mar. 05, 2019  shares | Nov. 08, 2018  $ / shares  shares | Nov. 05, 2018  $ / shares  shares | Jul. 31, 2020  USD ($) | Apr. 30, 2021  USD ($)  shares | Apr. 30, 2020  shares | Jun. 08, 2020  shares | Jun. 07, 2019  shares | Jun. 03, 2019  shares | |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Common stock issued for warrants exercised for cash | $ | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 1,081,792 | Ìý | Ìý | Ìý | Ìý | 
| Modification charge for warrants exercised | $ | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 25,966 | $ 25,966 | Ìý | Ìý | Ìý | Ìý | 
| Cashless exercise of warrants (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 164,929 | Ìý | Ìý | Ìý | 
| Number of investors | investor | Ìý | Ìý | 2 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Common stock, shares issued (in shares) | Ìý | 21,770,520 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 25,066,297 | 21,770,520 | Ìý | Ìý | Ìý | 
| Senior Loans | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Granted (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | 200,000 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Investor | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Common stock issued for cashless warrant exercise (in shares) | Ìý | Ìý | Ìý | 6,271 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Investor | Warrant | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Cashless exercise of warrants (in shares) | Ìý | Ìý | Ìý | 13,542 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Investor 1 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Common stock issued for cashless warrant exercise (in shares) | Ìý | Ìý | 8,970 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Investor 1 | Warrant | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Cashless exercise of warrants (in shares) | Ìý | Ìý | 18,818 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Investor 2 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Common stock issued for cashless warrant exercise (in shares) | Ìý | Ìý | 42,285 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Investor 2 | Warrant | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Cashless exercise of warrants (in shares) | Ìý | Ìý | 88,710 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Former Director | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Common stock, shares issued (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 9,806 | 
| Former Director | Warrant | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Common stock, shares issued (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 21,930 | 
| Chief Executive Officer | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Common stock, shares issued (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 9,597 | Ìý | 
| Advisory Board Member | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Granted (in shares) | Ìý | 50,000 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Weighted average recognition period | Ìý | 3 years | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Loan Agreements | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Warrants granted, exercise price (in dollars per share) | $ / shares | Ìý | Ìý | Ìý | Ìý | $ 6.00 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Revolving Credit Facility | Credit Facility Agreement | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Exercise price (in dollars per share) | $ / shares | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 5.85 | $ 5.85 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Class of warrant or right, number of securities called by warrants or rights (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 92,049 | 92,049 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Warrant term | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 5 years | 5 years | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Cooperman Warrants | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Decrease in exercise price of common stock purchase warrants | 5.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Class of warrant or right, number of securities called by warrants or rights (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 192,049 | Ìý | Ìý | 
| Cooperman Warrants | Loan Agreements | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Warrants granted, exercise price (in dollars per share) | $ / shares | $ 5.70 | Ìý | Ìý | Ìý | $ 6.00 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Cooperman Warrants | Revolving Credit Facility | Credit Facility Agreement | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 
| Exercise price (in dollars per share) | $ / shares | $ 5.56 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 5.85 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |