Aggregate potential clinical milestone payments available to be earned under collaboration agreement.

No definition available.

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Data Type:	xbrli:monetaryItemType
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- Definition

Aggregate potential regulatory milestone payments available to be earned under a collaboration arrangement.

+ References

No definition available.

+ Details

Name:	mgnx_AdditionalPotentialRegulatoryMilestonePaymentsUnderAgreement
Namespace Prefix:	mgnx_
Data Type:	xbrli:monetaryItemType
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- Definition

Aggregate potential sales milestone payments available to be earned under collaboration agreement.

+ References

No definition available.

+ Details

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- Definition

Portion of consideration allocated to equity.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Portion of consideration allocated to license and pre-clinical research and development.

+ References

No definition available.

+ Details

Name:	mgnx_AmountAllocatedToLicenseAndRD
Namespace Prefix:	mgnx_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Clinical milestone earned during the period

+ References

No definition available.

+ Details

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- Definition

Initial fee received from collaboration or license agreement.

+ References

No definition available.

+ Details

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Balance Type:	credit
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- Definition

Amount by which purchase price exceeds fair value for common stock purchased by collaborator.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Total consideration received under agreement.

+ References

No definition available.

+ Details

Name:	mgnx_TotalConsideration
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Revenue earned during the period relating to consideration received from another party for the right to use, but not own, certain of the entity's intangible assets. Licensing arrangements include, but are not limited to, rights to use a patent, copyright, technology, manufacturing process, software or trademark. Licensing fees are generally, but not always, fixed as to amount and not dependent upon the revenue generated by the licensing party. An entity may receive licensing fees for licenses that also generate royalty payments to the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(e))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Cash received on stock transaction after deduction of issuance costs.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

No definition available.

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
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- Details

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Period Type:

Collaboration and Other Agreements, Janssen Biotech, Inc. (Details) - Janssen Biotech, Inc. [Member] - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 31, 2015	Sep. 30, 2015	Sep. 30, 2015	Jul. 31, 2015
Collaboration and Other Agreements [Line Items]
Sale of common stock (in shares)	1,923,077
Sale of common stock (in dollars per share)	$ 39.00
Proceeds of stock sale	$ 75.0
Additional Potential Clinical Milestone Payments Under Agreement		$ 205.0	$ 205.0
Additional Potential Regulatory Milestone Payments Under Agreement		220.0	220.0
Additional Potential Sales Milestone Payments Under Agreement		150.0	150.0
Premium received on stock purchase	12.3
Recognized revenue under agreement		$ 10.0	$ 72.3
Non-refundable upfront payment	50.0
Amount allocated to equity	62.7
Amount allocated to license and R&D	62.3
Total consideration	$ 125.0
Clinical milestone earned during period				$ 10.0