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Share-based compensation - Range of exercise prices in stock options (Details) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 shares $ / shares | Dec. 31, 2019 shares $ / shares | Dec. 31, 2018 shares $ / shares
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Weighted average remaining contractual life (years) | 2 years 6 months 10 days |  |
Number of stock options outstanding (in shares) | shares | 173,251 | 200,631 | 198,221
Weighted average exercise price (in usd per option) | $ 49.44 | $ 49.07 | $ 48.55
Number of stock options exercisable (in shares) | shares | 146,303 |  |
Weighted average exercise price, exercisable options (in usd per option) | $ 51.06 |  |
$29.27 to $35.51 |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Weighted average remaining contractual life (years) | 3 years 1 month 20 days |  |
Number of stock options outstanding (in shares) | shares | 63,307 |  |
Weighted average exercise price (in usd per option) | $ 33.29 |  |
Number of stock options exercisable (in shares) | shares | 47,867 |  |
Weighted average exercise price, exercisable options (in usd per option) | $ 34.59 |  |
$29.27 to $35.51 | Bottom of range |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Exercise price of outstanding share options (usd per share) | 29.27 |  |
$29.27 to $35.51 | Top of range |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Exercise price of outstanding share options (usd per share) | $ 35.51 |  |
$45.40 to $50.17 |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Weighted average remaining contractual life (years) | 3 years 2 months 1 day |  |
Number of stock options outstanding (in shares) | shares | 24,034 |  |
Weighted average exercise price (in usd per option) | $ 50.17 |  |
Number of stock options exercisable (in shares) | shares | 24,034 |  |
Weighted average exercise price, exercisable options (in usd per option) | $ 50.17 |  |
$45.40 to $50.17 | Bottom of range |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Exercise price of outstanding share options (usd per share) | 45.40 |  |
$45.40 to $50.17 | Top of range |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Exercise price of outstanding share options (usd per share) | $ 50.17 |  |
$54.65 to $78.59 |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Weighted average remaining contractual life (years) | 1 year 10 months 20 days |  |
Number of stock options outstanding (in shares) | shares | 85,910 |  |
Weighted average exercise price (in usd per option) | $ 61.13 |  |
Number of stock options exercisable (in shares) | shares | 74,402 |  |
Weighted average exercise price, exercisable options (in usd per option) | $ 61.94 |  |
$54.65 to $78.59 | Bottom of range |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Exercise price of outstanding share options (usd per share) | 54.65 |  |
$54.65 to $78.59 | Top of range |  |  |
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items] |  |  |
Exercise price of outstanding share options (usd per share) | $ 78.59 |  |

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