FAIR VALUE MEASUREMENTS, Initial Measurement (FY) (Details) - Initial Public Offering [Member]	Sep. 17, 2020 shares
Public Warrants [Member]
Initial Measurement [Abstract]
Number of securities called by each unit (in shares)	0.5
Class A Common Stock [Member]
Initial Measurement [Abstract]
Number of securities called by each unit (in shares)	1

The number of securities into which each unit may be converted. For example, but not limited to, each unit may be converted into two shares of common stock.

No definition available.

Name:	sbg_UnitsNumberOfSecuritiesCalledByUnits
Namespace Prefix:	sbg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant