Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS The Chairman, Chief Executive Officer and President, the Executive Vice President of Real Estate, the Executive Vice President-Chief Legal and Administrative Officer and the Senior Vice President-Chief Accounting Officer of the Company are also officers of various members of the Saul Organization and their management time is shared with the Saul Organization. Their annual compensation is fixed by the Compensation Committee of the Board of Directors, with the exception of the Senior Vice President-Chief Accounting Officer whose share of annual compensation allocated to the Company is determined by the shared services agreement (described below). The Company participates in a multiemployer 401K plan with entities in the Saul Organization which covers those full-time employees who meet the requirements as specified in the plan. Company contributions, which are included in general and administrative expense or property operating expenses in the consolidated statements of operations, at the discretionary amount of up to 6% of the employee’s cash compensation, subject to certain limits, were $302,000, $322,200, and $345,900, for 2020, 2019, and 2018, respectively. All amounts deferred by employees and contributed by the Company are fully vested. The Company also participates in a multiemployer nonqualified deferred compensation plan with entities in the Saul Organization which covers those full-time employees who meet the requirements as specified in the plan. According to the plan, which can be modified or discontinued at any time, participating employees defer 2% of their compensation in excess of a specified amount and the Company matches those deferrals up to three times the amount deferred by employees. The Company’s expense, included in general and administrative expense, totaled $241,300, $345,200, and $282,500, for the years ended December 31, 2020, 2019, and 2018, respectively. All amounts deferred by employees and the Company are fully vested. The cumulative unfunded liability under this plan was $2.9 million and $3.1 million, at December 31, 2020 and 2019, respectively, and is included in accounts payable, accrued expenses and other liabilities in the consolidated balance sheets. The Company has entered into a shared services agreement (the “Agreement”) with the Saul Organization that provides for the sharing of certain personnel and ancillary functions such as computer hardware, software, and support services and certain direct and indirect administrative personnel. The method for determining the cost of the shared services is provided for in the Agreement and is based upon head count, estimates of usage or estimates of time incurred, as applicable. Senior management has determined that the final allocations of shared costs are reasonable. The terms of the Agreement and the payments made thereunder are reviewed annually by the Audit Committee of the Board of Directors, which consists entirely of independent directors. Net billings by the Saul Organization for the Company’s share of these ancillary costs and expenses for the years ended December 31, 2020, 2019, and 2018, which included rental expense for the Company’s headquarters lease (see Note 7. Long Term Lease Obligations), totaled $7.4 million, $8.4 million, and $8.4 million, respectively. The amounts are expensed when incurred and are primarily reported as general and administrative expenses or capitalized to specific development projects in these consolidated financial statements. As of December 31, 2020 and 2019, accounts payable, accrued expenses and other liabilities included $782,700 and $918,700, respectively, representing billings due to the Saul Organization for the Company’s share of these ancillary costs and expenses. The Company has entered into a shared third-party predevelopment cost agreement with the Saul Trust (the “Predevelopment Agreement”). The Predevelopment Agreement, which expired on December 31, 2015 and was extended to December 31, 2016, relates to the sharing of third-party predevelopment costs incurred in connection with the planning of the future redevelopment of certain adjacent real estate assets in the Twinbrook area of Rockville, Maryland. On December 8, 2016, the Company entered into a replacement agreement with the Saul Trust which extended the expiration date to December 31, 2017 and provides for automatic twelve month renewals unless either party provides notice of termination. The costs will be shared on a pro rata basis based on the acreage owned by each entity and neither party is obligated to advance funds to the other. On November 5, 2019, the Company entered into a Contribution Agreement to acquire the Contributed Property from the Saul Trust. In exchange for the Contributed Property, the Company will issue to the Saul Trust 1,416,071 limited partnership units. In connection with the contribution, the Company is obligated to reimburse the Saul Trust for certain pre-development and carrying costs incurred by the Saul Trust subsequent to the date of the Contribution Agreement, which total approximately $6.1 million as of December 31, 2020. Deed to the Contributed Property and the units were placed in escrow until certain conditions of the Contribution Agreement are satisfied. The B. F. Saul Insurance Agency of Maryland, Inc., a subsidiary of the B. F. Saul Company and a member of the Saul Organization, is a general insurance agency that receives commissions and counter-signature fees in connection with the Company’s insurance program. Such commissions and fees amounted to approximately $427,700, $399,600, and $407,900, for the years ended December 31, 2020, 2019, and 2018, respectively. In August 2016, the Company entered into an agreement to acquire from the Saul Trust approximately 13.7 acres of land located at the intersection of Ashburn Village Boulevard and Russell Branch Parkway in Ashburn, Virginia. The transaction closed on May 9, 2018, and the Company issued 176,680 limited partnership units to the Saul Trust. The Company constructed a shopping center, Ashbrook Marketplace, and may be obligated to issue additional limited partnership units to the Saul Trust in the second quarter of 2021. As of December 31, 2020, the Company estimates this obligation to range in value from $3.3 million to $3.6 million, based on projected net operating income of Ashbrook Marketplace for the 12 months ending May 31, 2021.