| Year ended December 31, 2017 | |||||||||||||||||
| Amount of options | Weighted average exercise price | Weighted average remaining contractual life (in years) | Aggregate intrinsic value | ||||||||||||||
| Outstanding at January 1, 2017 | 2,137,783 | 6.91 | 3.43 | 15,171 | |||||||||||||
| Granted | 880,000 | 11.53 | |||||||||||||||
| Exercised | (722,483 | ) | 3.40 | ||||||||||||||
| Expired and forfeited | (187,887 | ) | 9.71 | ||||||||||||||
| Outstanding at December 31, 2017 | 2,107,413 | 9.67 | 4.25 | 24,749 | |||||||||||||
| Exercisable at December 31, 2017 | 783,663 | 7.05 | 2.70 | 9,028 | |||||||||||||