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Financial instruments and risk management - Risk management (Details) | 12 Months Ended
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Mar. 31, 2013 | Mar. 31, 2012 | Mar. 31, 2011
Concentration Risk [Line Items] |  |  |
General payment terms | 30 days |  |
Trade accounts receivables | Geographic concentration risk | Western Canada |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 100.00% | 95.00% |
Customer A | Total revenues | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 25.00% | 15.00% | 30.00%
Customer A | Accounts receivable and unbilled revenue | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 23.00% | 4.00% |
Customer B | Total revenues | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 23.00% | 23.00% | 10.00%
Customer B | Accounts receivable and unbilled revenue | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 20.00% | 31.00% |
Customer C | Total revenues | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 17.00% | 6.00% | 0.00%
Customer C | Accounts receivable and unbilled revenue | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 11.00% | 10.00% |
Customer D | Total revenues | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 8.00% | 10.00% | 13.00%
Customer D | Accounts receivable and unbilled revenue | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 11.00% | 4.00% |
Customer E | Total revenues | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 6.00% | 31.00% | 38.00%
Customer E | Accounts receivable and unbilled revenue | Major customers |  |  |
Concentration Risk [Line Items] |  |  |
Concentration risk, percentage | 8.00% | 11.00% |

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- Definition Accounts Receivable, General Payment Terms + References No definition available. + Details
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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13537-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611 + Details
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