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Share capital (Share Issuances) (Narrative) (Details) - USD ($) | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of classes of share capital [line items] |  |  |  |
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 | $ 1.5 | $ 1.58 |  |
Shares outstanding, amount | $ 89,709,000 | $ 87,447,000 | $ 88,058,000 | $ 87,144,000
Restricted Share [Member] |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |
Shares outstanding, share | 86,692 |  | 208,722 |
Shares outstanding, amount | $ 200,000 |  | $ 800,000 |
Deferred Share Units [Member] |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |
Shares outstanding, share | 314,029 |  | 286,920 |
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% |  |  |

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