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Financial instruments and risk management - Financial instruments (Details) (CAD) | 12 Months Ended |
--- | --- | ---
Mar. 31, 2013 | Mar. 31, 2012
Carrying Amount |  |  |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |  |  |
Capital lease obligations | 41,822,000 | [1] | 10,701,000 | [1]
Series 1 Debentures | 225,000,000 | [2] | 225,000,000 | [2]
Fair Value |  |  |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |  |  |
Capital lease obligations | 37,369,000 | [1] | 10,657,000 | [1]
Series 1 Debentures | 220,079,000 | [2] | 203,624,000 | [2]
Credit facilities |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Outstanding balance, long-term debt | 45,200,000 |  | 78,800,000 |
Change in annual interest expense as a result of 100 basis point change to interest rates | 500,000 |  |  |
[1] | The fair values of amounts due under capital leases are based on management estimates which are determined by discounting cash flows required under the instruments at the interest rates currently estimated to be available for instruments with similar terms.
[2] | The fair value of the Series 1 Debentures is based upon the expected discounted cash flows and the period end market price of similar financial instruments.

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- Definition This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13476-108611 + Details
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