Warrant Liability - Additional Information (Details) - shares	Feb. 28, 2022	Dec. 31, 2021	Dec. 31, 2017
Warrant Liability.
Warrants To Be Modified, Number			952,184
Warrants To Be Re-measured, Number		92,212	1,044,396
Warrants expired and unexercised	92,212

Number of share warrants (or share units) expired and unexercised during the current period.

No definition available.

Name:	bstg_SharebasedCompensationArrangementBySharebasedPaymentAwardWarrantsExpired
Namespace Prefix:	bstg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant