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Financial instruments and risk management - Maximum credit exposure (Details) (CAD) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Unbilled revenue | 43,622 us-gaap_UnbilledContractsReceivable | 32,168 us-gaap_UnbilledContractsReceivable
Maximum exposure to credit risk |  |
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items] |  |
Trade accounts receivables | 65,474 noa_FairValueConcentrationOfRiskTradeAccountsReceivable / us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis = us-gaap_FairValueConcentrationOfRiskMaximumAmountOfLossMember | 68,364 noa_FairValueConcentrationOfRiskTradeAccountsReceivable / us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis = us-gaap_FairValueConcentrationOfRiskMaximumAmountOfLossMember
Other receivables | 1,029 noa_FairValueConcentrationOfRiskOtherReceivables / us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis = us-gaap_FairValueConcentrationOfRiskMaximumAmountOfLossMember | 1,813 noa_FairValueConcentrationOfRiskOtherReceivables / us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis = us-gaap_FairValueConcentrationOfRiskMaximumAmountOfLossMember
Total accounts receivable | 66,503 us-gaap_FairValueConcentrationOfRiskAccountsReceivable / us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis = us-gaap_FairValueConcentrationOfRiskMaximumAmountOfLossMember | 70,177 us-gaap_FairValueConcentrationOfRiskAccountsReceivable / us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis = us-gaap_FairValueConcentrationOfRiskMaximumAmountOfLossMember
Unbilled revenue | 43,622 us-gaap_UnbilledContractsReceivable / us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis = us-gaap_FairValueConcentrationOfRiskMaximumAmountOfLossMember | 32,168 us-gaap_UnbilledContractsReceivable / us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis = us-gaap_FairValueConcentrationOfRiskMaximumAmountOfLossMember

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- Definition This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 3 -Subparagraph a, b -Article 5 + Details
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- Definition Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3(c)(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph c(3) -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 912 -SubTopic 310 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6471842&loc=d3e55302-109406 + Details
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