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Share capital - Stock Options Rollforward (Details) shares in Thousands | 12 Months Ended
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Dec. 31, 2018 CAD ($) shares | Dec. 31, 2017 CAD ($) shares
Disclosure of share capital, reserves and other equity interest [Abstract] |  |
Number of outstanding options, beginning of year (in shares) | shares | 57,602 | 50,410
Number of options granted (in shares) | shares | 25,380 | 22,968
Number of options exercised (in shares) | shares | (12,347) | (13,708)
Number of options forfeited (in shares) | shares | (3,003) | (2,068)
Number of outstanding options, ending of year (in shares) | shares | 67,632 | 57,602
Weighted-average exercise price, beginning of year (in Cdn.$per share) | $ | $ 2.70 | $ 2.24
Weighted average exercise price, options granted (in Cdn.$per share) | $ | 3.35 | 3.65
Weighted average exercise price, options exercised (in Cdn.$per share) | $ | 2.40 | 2.54
Weighted average exercise price, options forfeited (in Cdn.$per share) | $ | 3.50 | 3.27
Weighted-average exercise price, end of year (in Cdn.$per share) | $ | $ 2.96 | $ 2.70

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- Definition The number of share options outstanding in a share-based payment arrangement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 45 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_45_d&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 45 -Subparagraph b -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_45_b_i&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 45 -Subparagraph b -Clause vi -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_45_b_vi&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The number of share options exercised in a share-based payment arrangement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 45 -Subparagraph b -Clause iv -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_45_b_iv&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The number of share options forfeited in a share-based payment arrangement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 45 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_45_b_iii&doctype=Standard -URIDate 2017-03-09 + Details
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