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v2.4.1.9

Lease Exit Liability - Additional Information (Detail) (USD $) | 12 Months Ended | 0 Months Ended |
--- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Jul. 16, 2014 | Jul. 16, 2008
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Operating Lease | 2018 |  |  |  |
Onetime purchase payment under purchase agreement |  |  |  |  | $ 5,000,000 mgnx_OnetimeMilestonePaymentToBePaidUnderAgreement
Additional amounts recorded | 0 mgnx_ContingentConsiderationRecordedAsIncrementalInProcessResearchAndDevelopmentExpense | 0 mgnx_ContingentConsiderationRecordedAsIncrementalInProcessResearchAndDevelopmentExpense | 0 mgnx_ContingentConsiderationRecordedAsIncrementalInProcessResearchAndDevelopmentExpense |  |
Minimum [Member] |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Onetime payment paid under license of product |  |  |  |  | 8,000,000 mgnx_OnetimeMilestonePaymentToBePaidUnderAgreementUponSpecifiedLevelOfSalesOfProducts / us-gaap_RangeAxis = us-gaap_MinimumMember
Maximum [Member] |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Onetime payment paid under license of product |  |  |  |  | $ 12,000,000 mgnx_OnetimeMilestonePaymentToBePaidUnderAgreementUponSpecifiedLevelOfSalesOfProducts / us-gaap_RangeAxis = us-gaap_MaximumMember
Series D Convertible Preferred Stock [Member] |  |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |  |
Shares issued in connection with acquisition |  |  |  | 12,466,039 us-gaap_StockIssuedDuringPeriodSharesAcquisitions / us-gaap_StatementClassOfStockAxis = mgnx_ConvertiblePreferredStockSeriesDMember |

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- Definition Contingent consideration recorded as incremental in process research and development expense. + References No definition available. + Details
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- Definition Lease expiration year. + References No definition available. + Details
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- Definition One-time milestone payment to be paid under agreement. + References No definition available. + Details
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- Definition One-time milestone payment to be paid under agreement upon specified level of sales of products. + References No definition available. + Details
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- Definition Number of shares of stock issued during the period pursuant to acquisitions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.28,29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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- Details
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