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Share Capital (Equity Financing) (Details) $ / shares in Units, $ in Millions |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Feb. 09, 2017 USD ($) $ / shares shares | Dec. 31, 2017 CAD / shares | Dec. 31, 2016 CAD / shares
Equity Financing [Line Items] |  |  |
Equity financing (in shares) | shares | 31,450,000 |  |
Share price (usd per share) | (per share) | $ 7.95 | CAD 9.40 | CAD 8.78
Gross proceeds from equity financing | $ 250.0 |  |
Transaction costs, equity financing | 10.9 |  |
Equity Financing [Member] |  |  |
Equity Financing [Line Items] |  |  |
Deferred tax assets | $ 2.7 |  |

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