Financial instruments measured at fair value
| Fair value measurements at December 31, 2017 using | ||||||||||||
| Level 1 | Level 2 | Level 3 | ||||||||||
| Financial liabilities | ||||||||||||
| Derivative financial liabilities – convertible promissory notes | $ | – | $ | 1,859,700 | $ | – | ||||||
| Fair value measurements at December 31, 2016 using | ||||||||||||
| Level 1 | Level 2 | Level 3 | ||||||||||
| Financial liabilities | ||||||||||||
| Derivative financial liabilities – convertible promissory notes | $ | – | $ | 794,235 | $ | – | ||||||
| Fair value measurements at December 31, 2015 using | ||||||||||||
| Level 1 | Level 2 | Level 3 | ||||||||||
| Financial liabilities | $ | $ | $ | |||||||||
| Derivative financial liabilities – convertible promissory notes | – | 2,568,188 | – | |||||||||
| Derivative financial liabilities – interest rate swap agreement | – | 165,648 | – | |||||||||
| Total financial liabilities | $ | – | $ | 2,733,836 | $ | – | ||||||