SAFE Agreements - Additional Information (Details) $ in Thousands	3 Months Ended
Mar. 31, 2021 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Change in fair value of SAFEs	$ (2,492)

Gain loss due to change in fair value of simple agreement for future equity.

No definition available.

Name:	bttx_GainLossDueToChangeInFairValueOfSimpleAgreementForFutureEquity
Namespace Prefix:	bttx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration