| | | | | | | | | | | Spot exchange rate at | | |||||||
| | Average exchange rate | | December 31, | | ||||||||||||||
| | 2017 | | 2016 | | 2015 | | 2017 | | 2016 | | 2015 | | ||||||
Dollars | | $ | 18.91 | | | 18.68 | | | 15.87 | | | 19.66 | | | 20.64 | | | 17.21 | |