SAFE Agreements - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Change in fair value of SAFEs	$ (2,821)	$ (5,313)

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