Revenue from Contracts with Customers - Schedule of Revenue Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$ 0	$ 1,473	$ 0	$ 951

Contract with customer liability revenue recognized with related party.

No definition available.

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