Selected Balance Sheet Information - Schedule of Accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Selected Balance Sheet Information
Accrued clinical consulting services	$ 807	$ 696
Accrued vendor payments	492	1,028
Accrued manufacturing costs	197	204
Total	$ 1,496	$ 1,928

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

No definition available.

Name:	syn_AccruedLiabilitiesCurrent.
Namespace Prefix:	syn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant