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Real Estate Transactions - Narrative (Details) |  |  |  | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2021 USD ($) shares | Jun. 29, 2021 USD ($) shares | Nov. 05, 2019 a shares | Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) | Mar. 05, 2021 USD ($) a | Dec. 31, 2020 USD ($) | Jan. 01, 2019 leaseExtensionOption
Real Estate [Line Items] |  |  |  |  |  |  |  |
Assets placed in service | $ 2,266,362,000 |  |  | $ 2,266,362,000 |  |  | $ 2,124,796,000 |
Lease renewal term |  |  |  |  |  |  |  | 5 years
Right-of-use asset | 321,900 |  |  | 321,900 |  |  |  |
Operating lease liability | 334,500 |  |  | 334,500 |  |  |  |
Deferred leasing costs, net | 24,638,000 |  |  | 24,638,000 |  |  | 26,872,000 |
Accumulated amortization deferred leasing cost | $ 47,700,000 |  |  | 47,700,000 |  |  | $ 44,500,000 |
Depreciation expense |  |  |  | 34,200,000 | $ 33,600,000 |  |  |
Repairs and maintenance expense |  |  |  | 10,200,000 | 8,000,000 |  |  |
Impairment of real estate |  |  |  | $ 0 |  |  |  |
Business acquisition, expenses reimbursed |  |  |  |  |  | $ 7,400,000 |  |
Operating lease, incremental borrowing rate |  |  |  | 5.63% |  |  |  |
Finance lease, right-of-use asset, amortization |  |  |  | $ 104,000 |  |  |  |
Finance lease, interest expense |  |  |  | $ 362,800 |  |  |  |
Contribution Agreement |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Right-of-use asset |  |  |  |  |  | 19,400,000 |  |
Operating lease liability |  |  |  |  |  | 19,400,000 |  |
Number of partnership units issued in transaction (in shares) | shares |  |  | 1,416,071 |  |  |  |  |
Business acquisition, transaction costs |  |  |  |  |  | $ 1,200,000 |  |
Leasehold Interest Contributed In Contribution Agreement |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Number of partnership units issued in transaction (in shares) | shares | 469,740 |  |  |  |  |  |  |
Asset acquisition consideration transferred |  | $ 21,500,000 |  |  |  |  |  |
Payments to acquire businesses, gross |  | $ 700,000 |  |  |  |  |  |
Leasehold Interest Contributed In Contribution Agreement | Limited Partner |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Number of partnership units issued in transaction (in shares) | shares |  | 469,740 |  |  |  |  |  |
BF Saul Real Estate Investment Trust | Contribution Agreement |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Area of land | a |  |  | 10.3 |  |  |  |  |
Minimum |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Operating lease term of contract | 1 year |  |  | 1 year |  |  |  |
Maximum |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Operating lease term of contract | 15 years |  |  | 15 years |  |  |  |
Building | Minimum |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  |  |  | 35 years |  |  |  |
Building | Maximum |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  |  |  | 50 years |  |  |  |
Building Improvements | Maximum |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  |  |  | 20 years |  |  |  |
Lease Acquisition Costs |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Amortization of intangible assets |  |  |  | $ 3,600,000 | $ 4,000,000 |  |  |
The Waycroft and Ashbrook Marketplace |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Assets placed in service | $ 8,700,000 |  |  | $ 8,700,000 |  |  |  |
Corporate Headquarters |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Number of options to extend lease | leaseExtensionOption |  |  |  |  |  |  |  | 1
Twinbrook Metro Station | BF Saul Real Estate Investment Trust | Contribution Agreement |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Area of land | a |  |  | 6.8 |  |  | 6.8 |  |
Twinbrook Metro Station Leasehold Interest | BF Saul Real Estate Investment Trust | Contribution Agreement |  |  |  |  |  |  |  |
Real Estate [Line Items] |  |  |  |  |  |  |  |
Area of land | a |  |  | 1.3 |  |  | 1.3 |  |

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