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Stock-based compensation - Options by exercise price range (Details) - Share option plan - CAD / shares | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Options outstanding, Number (in shares) | 1,448,000 |
Options outstanding, Weighted average remaining life | 5 years 5 months | 6 years 1 month
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 5.33 | CAD 5.87
Options exercisable | 886,220 | 824,720
Options exercisable, Weighted average remaining life | 4 years 7 months |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 6.52 | CAD 8.41
$2.75 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 2.75 |
Options outstanding, Number (in shares) | 288,900 |
Options outstanding, Weighted average remaining life | 6 years 5 months |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 2.75 |
Options exercisable, Number (in shares) | 149,420 |
Options exercisable, Weighted average remaining life | 6 years 6 months |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 2.75 |
$2.79 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 2.79 |
Options outstanding, Number (in shares) | 450,000 |
Options outstanding, Weighted average remaining life | 6 years 6 months 12 days |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 2.79 |
Options exercisable, Number (in shares) | 150,000 |
Options exercisable, Weighted average remaining life | 6 years 6 months 12 days |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 2.79 |
$3.69 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 3.69 |
Options outstanding, Number (in shares) | 29,100 |
Options outstanding, Weighted average remaining life | 2 years 10 months 24 days |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 3.69 |
Options exercisable, Number (in shares) | 29,100 |
Options exercisable, Weighted average remaining life | 2 years 10 months 24 days |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 3.69 |
$4.90 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 4.90 |
Options outstanding, Number (in shares) | 40,000 |
Options outstanding, Weighted average remaining life | 6 years 3 months |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 4.90 |
Options exercisable, Number (in shares) | 24,000 |
Options exercisable, Weighted average remaining life | 6 years 3 months |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 4.90 |
$5.00 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 5.00 |
Options outstanding, Number (in shares) | 127,760 |
Options outstanding, Weighted average remaining life | 4 months 18 days |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 5.00 |
Options exercisable, Number (in shares) | 127,760 |
Options exercisable, Weighted average remaining life | 4 months 18 days |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 5.00 |
$5.91 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 5.91 |
Options outstanding, Number (in shares) | 149,200 |
Options outstanding, Weighted average remaining life | 8 years |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 5.91 |
Options exercisable, Number (in shares) | 59,680 |
Options exercisable, Weighted average remaining life | 8 years |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 5.91 |
$6.56 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 6.56 |
Options outstanding, Number (in shares) | 79,860 |
Options outstanding, Weighted average remaining life | 5 years 11 months |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 6.56 |
Options exercisable, Number (in shares) | 63,080 |
Options exercisable, Weighted average remaining life | 5 years 11 months |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 6.56 |
$8.28 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 8.28 |
Options outstanding, Number (in shares) | 10,000 |
Options outstanding, Weighted average remaining life | 3 years 6 months |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 8.28 |
Options exercisable, Number (in shares) | 10,000 |
Options exercisable, Weighted average remaining life | 3 years 6 months |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 8.28 |
$8.58 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 8.58 |
Options outstanding, Number (in shares) | 30,000 |
Options outstanding, Weighted average remaining life | 4 years 8 months |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 8.58 |
Options exercisable, Number (in shares) | 30,000 |
Options exercisable, Weighted average remaining life | 4 years 8 months |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 8.58 |
$9.33 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 9.33 |
Options outstanding, Number (in shares) | 59,780 |
Options outstanding, Weighted average remaining life | 4 years 1 month |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 9.33 |
Options exercisable, Number (in shares) | 59,780 |
Options exercisable, Weighted average remaining life | 4 years 1 month |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 9.33 |
$10.13 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 10.13 |
Options outstanding, Number (in shares) | 59,060 |
Options outstanding, Weighted average remaining life | 5 years |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 10.13 |
Options exercisable, Number (in shares) | 59,060 |
Options exercisable, Weighted average remaining life | 5 years |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 10.13 |
$13.50 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 13.50 |
Options outstanding, Number (in shares) | 74,340 |
Options outstanding, Weighted average remaining life | 1 year 11 months |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 13.50 |
Options exercisable, Number (in shares) | 74,340 |
Options exercisable, Weighted average remaining life | 1 year 11 months |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 13.50 |
$16.46 |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Exercise price (CAD per share) | CAD 16.46 |
Options outstanding, Number (in shares) | 50,000 |
Options outstanding, Weighted average remaining life | 2 years 3 months |
Options outstanding, Weighted average exercise price (in CAD per share) | CAD 16.46 |
Options exercisable, Number (in shares) | 50,000 |
Options exercisable, Weighted average remaining life | 2 years 3 months |
Options exercisable, Weighted average exercise price (in CAD per share) | CAD 16.46 |

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- Definition The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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