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Share capital (Schedule of Stock Options Outstanding and Exercisable) (Details) shares in Thousands | Sep. 30, 2018 CAD ($) shares yr | Dec. 31, 2017 CAD ($) shares | Dec. 31, 2016 CAD ($) shares
--- | --- | --- | ---
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Outstanding | shares | 3,120 | 2,316 | 1,771
Weighted average exercise price | $ 3.79 | $ 3.06 | $ 4.64
Exercisable | shares | 1,849 |  |
Weighted average exercise price | $ 3.37 |  |
CAD 2.00 to 3.00 [Member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Weighted average remaining contractual life (years) | yr | 0.40 |  |
Outstanding | shares | 691 |  |
Weighted average exercise price | $ 2.04 |  |
Exercisable | shares | 691 |  |
Weighted average exercise price | $ 2.04 |  |
CAD 2.00 to 3.00 [Member] | Bottom of range [member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Exercise price | 2 |  |
CAD 2.00 to 3.00 [Member] | Top of range [member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Exercise price | $ 3 |  |
CAD 3.01 to 4.00 [Member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Weighted average remaining contractual life (years) | yr | 1.32 |  |
Outstanding | shares | 1,025 |  |
Weighted average exercise price | $ 3.85 |  |
Exercisable | shares | 683 |  |
Weighted average exercise price | $ 3.85 |  |
CAD 3.01 to 4.00 [Member] | Bottom of range [member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Exercise price | 3.01 |  |
CAD 3.01 to 4.00 [Member] | Top of range [member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Exercise price | $ 4 |  |
CAD 4.01 to 5.00 [Member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Weighted average remaining contractual life (years) | yr | 2.26 |  |
Outstanding | shares | 1,364 |  |
Weighted average exercise price | $ 4.58 |  |
Exercisable | shares | 462 |  |
Weighted average exercise price | $ 4.58 |  |
CAD 4.01 to 5.00 [Member] | Bottom of range [member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Exercise price | 4.01 |  |
CAD 4.01 to 5.00 [Member] | Top of range [member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Exercise price | $ 5 |  |
CAD 5.01 to 6.00 [Member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Weighted average remaining contractual life (years) | yr | 2.32 |  |
Outstanding | shares | 40 |  |
Weighted average exercise price | $ 5.55 |  |
Exercisable | shares | 13 |  |
Weighted average exercise price | $ 5.55 |  |
CAD 5.01 to 6.00 [Member] | Bottom of range [member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Exercise price | 5.01 |  |
CAD 5.01 to 6.00 [Member] | Top of range [member] |  |  |
Disclosure of range of exercise prices of outstanding share options [line items] |  |  |
Exercise price | $ 6 |  |

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