Stock Incentive Plans - Summary of Unvested Common Stock from Early Exercises Subject to Repurchase (Details)	3 Months Ended
Mar. 31, 2018 shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Unvested shares - January 1, 2018	265,098
Vested	(34,137)
Unvested shares - March 31, 2018	230,961

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