Development milestone payments.

No definition available.

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

- Definition

Percentage of costs owned under clinical trial programs.

+ References

No definition available.

+ Details

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

- Definition

Percentage of costs remaining under clinical trial programs.

+ References

No definition available.

+ Details

Name:	mcrb_PercentageOfCostsRemainingUnderClinicalTrialPrograms
Namespace Prefix:	mcrb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of performance identifiable deliverables.

+ References

No definition available.

+ Details

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Namespace Prefix:	mcrb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Regulatory payments.

+ References

No definition available.

+ Details

Name:	mcrb_RegulatoryPayments
Namespace Prefix:	mcrb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Revenue from reimbursement of development services.

+ References

No definition available.

+ Details

Name:	mcrb_RevenueFromReimbursementOfDevelopmentServices
Namespace Prefix:	mcrb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Sales based milestones.

+ References

No definition available.

+ Details

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

- Definition

Upfront payment in cash.

+ References

No definition available.

+ Details

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Namespace Prefix:	mcrb_
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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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The increase (decrease) during the reporting period, excluding the portion taken into income, in the liability reflecting revenue yet to be earned for which cash or other forms of consideration was received or recorded as a receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

+ Details

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

- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ 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=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Related Parties
-URI http://asc.fasb.org/extlink&oid=16382449

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

+ Details

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

- Details

Name:	us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis=mcrb_PhaseThreeClinicalTrialsMember
Namespace Prefix:
Data Type:	na
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- Details

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Collaboration Revenue - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	6 Months Ended
	Feb. 29, 2016	Jan. 31, 2016	Jun. 30, 2016	Jun. 30, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Period of performance identifiable deliverables		10 years
Collaboration revenue - related party			$ 3,004	$ 5,714
Deferred revenue				114,383
Phase 3 Clinical Trials [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of costs owned under clinical trial programs		67.00%
Nestlé Health Science [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment	$ 120,000			120,000
Development milestone payments		$ 295,000
Regulatory payments		365,000
Sales based milestones		$ 1,125,000
Percentage of costs remaining under clinical trial programs		33.00%
Reimbursement of development services				97
Collaboration revenue - related party			$ 3,004	5,714
Deferred revenue				$ 114,383