Fair Value Measurements - Additional Information (Details) - USD ($)	Jun. 30, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Assets, Level 1 and Level 2 transfers	$ 0	$ 0
Liabilities, Level 1 and Level 2 transfers	$ 0	$ 0

Fair value liabilities level one and level two transfers amount.

No definition available.

Name:	fdmt_FairValueLiabilitiesLevelOneAndLevelTwoTransfersAmount
Namespace Prefix:	fdmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant