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Stock-based compensation - Stock award plan (Details) (CAD) In Thousands, except Share data, unless otherwise specified | 12 Months Ended | 0 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2013 | Mar. 31, 2012 | Mar. 31, 2011 | Sep. 24, 2009 Stock award plan Chief Executive Officer | Mar. 31, 2013 Stock award plan Chief Executive Officer | Mar. 31, 2012 Stock award plan Chief Executive Officer | May 08, 2012 Stock award plan Chief Executive Officer | Nov. 08, 2011 Stock award plan Chief Executive Officer | May 08, 2011 Stock award plan Chief Executive Officer | Sep. 24, 2010 Stock award plan Chief Executive Officer
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items] |  |  |  |  |  |  |  |  |  |
Chief Executive Officer's employment agreement extension period |  |  |  | 2 years |  |  |  |  |  |
Common share rights granted to the former CEO |  |  |  |  |  |  | 50,000 | 50,000 | 50,000 | 150,000
Share of common stock issued upon settlement of stock awards |  |  |  |  | 50,000 | 100,000 |  |  |  |
Settlement of stock award plan | (148) | (822) | 0 |  | 148 | 822 |  |  |  |

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