| Year ended December 31 | 2017 | 2016 | 2015 | |||||||||||||||||||||
| Warrants |
Weighted average exercise price |
Warrants | Weighted average exercise price |
Warrants | Weighted average exercise price |
|||||||||||||||||||
| Balance, beginning of period | 941,969 | $ | 6.31 | 59,775 | $ | 2.20 | - | $ | - | |||||||||||||||
| Granted | - | - | 900,000 | 6.50 | 128,068 | $ | 2.20 | |||||||||||||||||
| Exercised | (41,969 | ) | (2.20 | ) | (17,806 | ) | (2.20 | ) | (68,293 | ) | $ | (2.20 | ) | |||||||||||
| Balance, end of period | 900,000 | $ | 6.50 | 941,969 | $ | 6.31 | 59,775 | $ | 2.20 | |||||||||||||||
| Warrants exercisable, end of period | 900,000 | $ | 6.50 | 941,969 | $ | 6.31 | 59,775 | $ | 2.20 | |||||||||||||||