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v3.19.1

Share-based compensation - Changes in SARs and TSARs (Details) | 12 Months Ended
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Dec. 31, 2018 USD ($) shares | Dec. 31, 2017 USD ($) shares
SARs |  |
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Number of outstanding units, beginning of period | shares | 1,450,077 | 1,511,485
Number of outstanding units granted | shares | 141,300 | 167,600
Number of outstanding units exercised | shares | (669,931) | (213,207)
Number of outstanding units cancelled | shares | (16,582) | (10,801)
Number of outstanding units expired | shares | (7,981) | (5,000)
Number of outstanding units, end of period | shares | 896,883 | 1,450,077
Exercise price of outstanding units, beginning of period (in usd per unit) | $ | $ 45.11 | $ 42.68
Exercise price of outstanding units granted (in usd per unit) | $ | 55.28 | 50.15
Exercise price of outstanding units exercised (in usd per unit) | $ | 39.00 | 32.03
Exercise price of outstanding units cancelled (in usd per unit) | $ | 53.12 | 50.18
Exercise price of outstanding units expired (in usd per unit) | $ | 28.74 | 25.22
Exercise price of outstanding units, end of period (in usd per unit) | $ | $ 51.27 | $ 45.11
TSARs |  |
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Number of outstanding units, beginning of period | shares | 2,043,495 | 2,416,111
Number of outstanding units granted | shares | 330,400 | 340,200
Number of outstanding units exercised | shares | (918,327) | (710,616)
Number of outstanding units cancelled | shares | (8,267) | (2,200)
Number of outstanding units expired | shares | 0 | 0
Number of outstanding units, end of period | shares | 1,447,301 | 2,043,495
Exercise price of outstanding units, beginning of period (in usd per unit) | $ | $ 46.62 | $ 42.10
Exercise price of outstanding units granted (in usd per unit) | $ | 55.37 | 50.17
Exercise price of outstanding units exercised (in usd per unit) | $ | 42.48 | 32.98
Exercise price of outstanding units cancelled (in usd per unit) | $ | 47.25 | 34.59
Exercise price of outstanding units expired (in usd per unit) | $ | 0.00 | 0.00
Exercise price of outstanding units, end of period (in usd per unit) | $ | $ 51.24 | $ 46.62

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