Stock Incentive Plans - Summary of Unvested Common Stock from Early Exercises Subject to Repurchase (Details)	9 Months Ended
Sep. 30, 2020 shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Unvested shares, Beginning Balance	21,666
Vested	(17,564)
Unvested shares, Ending Balance	4,102

Unvested common shares subject to repurchase outstanding.

No definition available.

Name:	fixx_UnvestedCommonSharesSubjectToRepurchaseOutstanding
Namespace Prefix:	fixx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant