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Share capital (Share Issuances) (Narrative) (Details) |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Jun. 14, 2016 USD ($) shares yr $ / shares | Jun. 14, 2016 CAD / shares | Jun. 09, 2016 USD ($) shares yr $ / shares | Jun. 09, 2016 CAD / shares | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 USD ($) shares | Dec. 31, 2015 USD ($)
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |
Shares and warrants issued on private placement, shares | shares | 3,210,416 |  | 5,555,555 |  |  |  |
Shares and warrants issued on private placement, sales price per share | CAD / shares |  | CAD 3.60 |  | CAD 3.60 |  |  |
Shares and warrants issued on private placement, proceeds | $ 9,000,000 |  | $ 15,700,000 |  |  |  |
Warrants issued on private placement, exercise price per share | (per share) | $ 4.68 |  |  | 4.68 |  |  |
Warrants issued on private placement, exercise period | yr | 5 |  | 5 |  |  |  |
Number of shares reserved for issuance as a percent of total common shares issued and oustanding |  |  |  |  | 10.00% |  |
Maximum term of stock options |  |  |  |  | Under the plan, the Board of Directors determines the term of a stock option to a maximum of 10 years |  |
Weighted average fair value at grant |  |  |  |  | $ 1.58 | $ 1.08 |
Shares outstanding, amount |  |  |  |  | $ 88,058,000 | $ 87,144,000 | $ 64,845,000
Restricted Share [Member] |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |
Shares outstanding, share | shares |  |  |  |  | 208,722 | 351,856 |
Shares outstanding, amount |  |  |  |  | $ 800,000 | $ 900,000 |
Deferred Share Units [Member] |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |
Shares outstanding, share | shares |  |  |  |  | 286,920 | 240,313 |
Shares outstanding, amount |  |  |  |  | $ 286,920 | $ 240,313 |
Deferred Share Units [Member] | Bottom of range [member] |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |
Percentage of quarterly director fee payments earned as awards of deferred share units |  |  |  |  | 20.00% |  |
Deferred Share Units [Member] | Top of range [member] |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |
Percentage of quarterly director fee payments earned as awards of deferred share units |  |  |  |  | 100.00% |  |
Broker [Member] |  |  |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |  |  |
Shares and warrants issued on private placement, sales price per share | CAD / shares |  |  |  | CAD 4.20 |  |  |
Warrants issued on private placement, exercise price per share | $ / shares | $ 4.20 |  | $ 4.68 |  |  |  |
Warrants issued on private placement, exercise period | yr | 2 |  | 2 |  |  |  |
Common share purchase warrants issued on private placement | shares | 224,728 |  | 388,886 |  |  |  |

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