| Basic and diluted net loss per share | 
    |  |  | Three Months Ended December 31, |  |  
    |  |  | 2018 |  |  | 2017 |  |  
    | Basic |  |  |  |  |  |  |  
    |  |  |  |  |  |  |  |  
    | Net income |  | $ | 1,530,509 |  |  | $ | 1,877,555 |  |  
    | Less: preferred stock dividends |  |  | (292 | ) |  |  | (292 | ) |  
    | Net income applicable to common stock |  | $ | 1,530,217 |  |  | $ | 1,877,263 |  |  
    |  |  |  |  |  |  |  |  |  |  
    | Weighted average common shares outstanding |  |  | 1,945,247 |  |  |  | 1,975,380 |  |  
    |  |  |  |  |  |  |  |  |  |  
    | Basic earnings per share |  | $ | 0.79 |  |  | $ | 0.95 |  |  
    |  |  |  |  |  |  |  |  |  |  
    | Diluted |  |  |  |  |  |  |  |  |  
    |  |  |  |  |  |  |  |  |  |  
    | Net income applicable to common stock |  | $ | 1,530,217 |  |  | $ | 1,877,263 |  |  
    | Add: preferred stock dividends |  |  | 292 |  |  |  | 292 |  |  
    | Net income applicable for diluted earnings per share |  | $ | 1,530,509 |  |  | $ | 1,877,555 |  |  
    |  |  |  |  |  |  |  |  |  |  
    | Weighted average common shares outstanding |  |  | 1,945,247 |  |  |  | 1,975,380 |  |  
    | Add: Options |  |  | 11,576 |  |  |  | 34,476 |  |  
    | Add: Series B Preferred Stock |  |  | 1,071,200 |  |  |  | 1,071,200 |  |  
    | Add: Series B Preferred Stock Warrants |  |  | 590,145 |  |  |  | 590,145 |  |  
    | Add: Series E Preferred Stock |  |  | 77,840 |  |  |  | 77,840 |  |  
    | Assumed weighted average common shares outstanding |  |  | 3,696,008 |  |  |  | 3,749,041 |  |  
    |  |  |  |  |  |  |  |  |  |  
    | Diluted earnings per share |  | $ | 0.41 |  |  | $ | 0.50 |  |  |