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Impact of COVID-19 - Consolidated Total Collections (Details) - Tenants	3 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021
Subsequent Event [Line Items]
Consolidated collections, percentage	0.99	0.99	0.99	0.99
Retail Real Estate
Subsequent Event [Line Items]
Consolidated collections, percentage	0.98	0.99	0.99	0.99
Office Real Estate
Subsequent Event [Line Items]
Consolidated collections, percentage	1	1	1	1
Residential Real Estate
Subsequent Event [Line Items]
Consolidated collections, percentage	0.99	0.99	0.99	0.99

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- Definition

Consolidated Collections, Percentage

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

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- 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

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Namespace Prefix:	us-gaap_
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Period Type:	duration

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- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=bfs_RetailRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=bfs_OfficeRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix:
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Balance Type:
Period Type: