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Share capital (Summary of Changes in Company's Outstanding Stock Options) (Details) shares in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 CAD ($) shares | Dec. 31, 2017 CAD ($) shares
Number |  |
Balance, beginning of year | shares | 2,316 | 1,771
Granted | shares | 1,395 | (1,058)
Exercised | shares | (471) | 261
Expired | shares | (120) | (252)
Balance, end of year | shares | 3,120 | 2,316
Weighted average exercise price |  |
Balance, beginning of year | $ | $ 3.06 | $ 4.64
Granted | $ | 4.61 | 3.86
Exercised | $ | 2.29 | 3.22
Expired | $ | 5.14 | 17.31
Balance, end of year | $ | $ 3.79 | $ 3.06

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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 2018-01-01 -Paragraph 45 -Subparagraph b -Clause iv -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2018-03-01&anchor=para_45_b_iv&doctype=Standard -URIDate 2018-03-16 + Details
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