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Related Party Transactions - Additional Information (Detail)			1 Months Ended		12 Months Ended
	Nov. 05, 2019 shares	Dec. 08, 2016	May 31, 2018 shares	Aug. 31, 2016 USD ($) a shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Related Party Transaction [Line Items]
Company contribution to a multi employer 401K plan at discretionary amount of employee's cash compensation, maximum percentage					6.00%	6.00%	6.00%
Company contribution to a multi employer 401K plan at discretionary amount of employee's cash compensation, amount					$ 302,000	$ 322,200	$ 345,900
Deferred compensation, employee contribution, percentage					2.00%
Deferred compensation, employer contribution, percentage					3	3	3
Deferred compensation, company contribution, amount					$ 241,300	$ 345,200	$ 282,500
Deferred compensation, cumulative unfunded liability					2,900,000	3,100,000
Ancillary costs and expenses					7,400,000	8,400,000	8,400,000
Liability due to the Saul Organization for the company's share of these ancillary costs and expenses					782,700	918,700
Automatic renewal period		12 months
Insurance commissions and fees expense					427,700	$ 399,600	$ 407,900
Contribution Agreement
Related Party Transaction [Line Items]
Number of partnership units issued in transaction (in shares) | shares	1,416,071
Estimated reimbursement of costs incurred					$ 6,100,000
BF Saul Real Estate Investment Trust | Ashbrook Marketplace
Related Party Transaction [Line Items]
Area of real estate property (in square feet) | a				13.7
Limited partnership units issued (in shares) | shares			176,680	176,680
BF Saul Real Estate Investment Trust | Ashbrook Marketplace | Minimum
Related Party Transaction [Line Items]
Noncash financial or equity instrument consideration, future shares issued estimated value				$ 3,300,000
BF Saul Real Estate Investment Trust | Ashbrook Marketplace | Maximum
Related Party Transaction [Line Items]
Noncash financial or equity instrument consideration, future shares issued estimated value				$ 3,600,000

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