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Organization, Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 USD ($) subsidiary shares | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Jan. 01, 2019 USD ($) agreement
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Number of subsidiaries interest owned in general and limited partnership | subsidiary | 2 |  |  |
Non-qualifying income related to real estate portfolio | $ 0 |  |  |
Amortization related to below-market lease | 2,500,000 | $ 2,000,000 | $ 1,500,000 |
Total amortization expense related to intangible assets | $ 19,200,000 | 17,700,000 | 15,900,000 |
Maturity period of highly-liquid investments at the time of purchase | three months or less |  |  |
Payments of deferred financing costs | $ (2,480,000) | (386,000) | (1,990,000) |
Total amortization expense related to deferred financing costs is included in interest expense | $ 1,641,000 | 1,445,000 | 1,713,000 |
Aggregate Deferred Rent Write Off |  | 200,000 | 0 |
Uncertain tax positions percentage | 50.00% |  |  |
Uncertain tax positions | $ 0 | 0 | 0 |
ARO liabilities accrued in connection with acquisitions | 164,000 | 0 | 0 |
Expenses recorded to general and administrative expense | 100,000 | 100,000 | 100,000 |
Aggregate undiscounted obligation on properties | 6,200,000 |  |  |
Right-of-use assets from operating leases | 5,794,000 |  |  |
Number of operating ground lease arrangements | agreement |  |  |  | 4
Above Market Leases |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Amortization related to above-market lease | $ 1,100,000 |  |  |
Amortization related to above-market lease |  | $ 1,100,000 | $ 700,000 |
Minimum |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Expected lease up period for estimating carrying costs | 9 months |  |  |
Remaining term of in-place leases and unamortized lease | 7 years |  |  |
REIT taxable income to its stockholders (as percent) | 90.00% |  |  |
Percentage of discount rate for calculating undiscounted obligation (as percent) | 2.50% |  |  |
Maximum |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Expected lease up period for estimating carrying costs | 18 months |  |  |
Remaining term of in-place leases and unamortized lease | 15 years |  |  |
REIT taxable income to its stockholders (as percent) | 100.00% |  |  |
Percentage of discount rate for calculating undiscounted obligation (as percent) | 7.00% |  |  |
Building and Improvements |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Estimated useful life | 39 years |  |  |
Equipment and Fixtures | Minimum |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Estimated useful life | 5 years |  |  |
Equipment and Fixtures | Maximum |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Estimated useful life | 20 years |  |  |
GCLP Business Trust I |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Subsidiary and business trust of the Company, formed under the laws of the Commonwealth of Massachusetts, date | Dec. 28, 2005 |  |  |
Percentage of limited partnership interest transferred to business unit (as percent) | 99.00% |  |  |
Number of trust shares exchanged for limited partnership interest (in shares) | shares | 100 |  |  |
Operating Partnership |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Company ownership percentage of voting securities | 98.60% | 97.50% |  |
Gladstone Commercial Advisers, Inc. |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Company ownership percentage of voting securities | 100.00% |  |  |
GCLP Business Trust II |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Percentage of limited partnership interest transferred to business unit (as percent) | 1.00% |  |  |
Number of trust shares exchanged for general partnership interest (in shares) | shares | 100 |  |  |
ASU 2016-02 |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Right-of-use assets from operating leases |  |  |  | $ 6,000,000
Weighted average discount rate (percent) |  |  |  | 5.34%
Number of fixed rental charges operating ground lease arrangements | agreement |  |  |  | 3
Number of variable charges operating ground lease arrangements | agreement |  |  |  | 1
Number of options to extend operating ground lease arrangements | agreement |  |  |  | 3
Number of early termination options operating ground lease arrangements | agreement |  |  |  | 1
ASU 2016-02 | Minimum |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Discount rate, basis spread on variable rate (percent) |  |  |  | 2.50%
ASU 2016-02 | Maximum |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |
Discount rate, basis spread on variable rate (percent) |  |  |  | 2.60%

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