Anticipated completion period for research and development projects.

No definition available.

Name:	sybx_AnticipatedCompletionOfResearchAndDevelopmentProjectsPeriod
Namespace Prefix:	sybx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Increase in transaction price of performance obligation of second phase.

+ References

No definition available.

+ Details

Name:	sybx_IncreaseInTransactionPriceOfPerformanceObligationOfSecondPhase
Namespace Prefix:	sybx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Initial milestone payment upon execution of amendment.

+ References

No definition available.

+ Details

Name:	sybx_InitialMilestonePaymentUponExecutionOfAmendment
Namespace Prefix:	sybx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Milestone payment on achievement of remaining milestone.

+ References

No definition available.

+ Details

Name:	sybx_MileStonePaymentOnAchievementOfRemainingMileStone
Namespace Prefix:	sybx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Milestone Payments

+ References

No definition available.

+ Details

Name:	sybx_MilestonePayments
Namespace Prefix:	sybx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of mile stone payments under second phase.

+ References

No definition available.

+ Details

Name:	sybx_NumberOfMileStonePaymentsUnderSecondPhase
Namespace Prefix:	sybx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Potential Milestone Payment

+ References

No definition available.

+ Details

Name:	sybx_PotentialMilestonePayment
Namespace Prefix:	sybx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Upfront payments.

+ References

No definition available.

+ Details

Name:	sybx_UpfrontPayments
Namespace Prefix:	sybx_
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

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118944033&loc=SL49130531-203044

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-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130549-203045

+ Details

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

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

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-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

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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

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AbbVie Collaboration Agreement - Additional Information (Detail) $ in Thousands			1 Months Ended		3 Months Ended		9 Months Ended
	Dec. 18, 2018 USD ($)	Sep. 27, 2018 USD ($) Milestone	May 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Feb. 28, 2019 USD ($)	Dec. 31, 2018 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognition of revenue					$ 305	$ 1,801	$ 993	$ 2,409
Current deferred revenue					1,775		1,775			$ 268
AbbVie Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of mile stone payments under second phase \| Milestone		2
Initial milestone payment upon execution of amendment		$ 2,000
Increase in transaction price of performance obligation of second phase	$ 2,000
Remaining milestone achieved									$ 2,500
Recognition of revenue					300	$ 1,800	1,000	$ 2,400
Current deferred revenue					$ 1,800		1,800
AbbVie Agreement \| IBDCo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront non-refundable payment				$ 2,000
Potential milestone payment							$ 16,500
Collaboration in research and development							54 months
Milestone payment			$ 2,000