Represents the percentage of cost sharing arrangement under collaborative and license agreements.

No definition available.

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Namespace Prefix:	mnta_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of net profit shared on sales of the product if no third-party competitors are marketing an interchangeable generic version of Product and Equivalent Product.

+ References

No definition available.

+ Details

Name:	mnta_CollaborativeArrangementPercentageOfProfitSharing
Namespace Prefix:	mnta_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Non-refundable upfront payment received under the term of Collaboration Agreement.

+ References

No definition available.

+ Details

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Namespace Prefix:	mnta_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of consideration recognized during the period for the milestone or milestones.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 28
-Section 50
-Paragraph 2
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=68058744&loc=SL6892177-166501

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Period Type:

Collaboration and License Agreements - CSL License and Option Agreement (Details) - CSL License Agreement - USD ($) $ in Millions			12 Months Ended
	Aug. 28, 2017	Jan. 05, 2017	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment		$ 50
Milestone payment on collaboration agreement	$ 298	$ 550
Percentage of cost sharing arrangement under collaborative and license agreements			50.00%
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of contractual profits earned under collaborative arrangement		50.00%
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of contractual profits earned under collaborative arrangement		30.00%