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Impact of COVID-19 - Narrative (Details)	3 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021
Tenants
Subsequent Event [Line Items]
Consolidated collections, percentage	0.99	0.99	0.99	0.99

X

- Definition

Consolidated Collections, Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	bfs_
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Balance Type:	na
Period Type:	duration

X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	srt_MajorCustomersAxis=bfs_TenantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: