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Organization, Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2016 USD ($) subsidiary shares | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
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 | 1,200,000 | $ 900,000 | $ 700,000
Total amortization expense related to intangible assets | $ 13,400,000 | 13,100,000 | 10,100,000
Maturity period of highly-liquid investments at the time of purchase | three months or less |  |
Payments of deferred financing costs | $ 1,500,000 | 1,880,000 | 1,029,000
Total amortization expense related to deferred financing costs is included in interest expense | 1,932,000 | 1,955,000 | 1,656,000
Deferred rent expense | $ 0 | 0 | 800,000
Uncertain tax positions percentage | 50.00% |  |
Uncertain tax positions | $ 0 | 0 | 0
Accrued liabilities | 0 | 56,000 | 405,000
Expenses recorded to general and administrative expense | 100,000 | 200,000 | 100,000
Aggregate undiscounted obligation on properties | 8,500,000 |  |
Expected payment to be made in next twelve months | 0 |  |
Expected payment to be made in second year | 0 |  |
Expected payment to be made in third year | 0 |  |
Expected payment to be made in fourth year | 0 |  |
Expected payment to be made in fifth year | 0 |  |
Above Market Leases [Member] |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |
Amortization related to above-market lease | $ 500,000 | 400,000 | 300,000
Minimum [Member] |  |  |
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 [Member] |  |  |
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 [Member] |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |
Estimated useful life | 39 years |  |
Equipment and Fixtures [Member] | Minimum [Member] |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |
Estimated useful life | 5 years |  |
Equipment and Fixtures [Member] | Maximum [Member] |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |
Estimated useful life | 20 years |  |
Building and Improvements [Member] |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |
Real estate depreciation expense | $ 24,100,000 | $ 22,200,000 | $ 18,800,000
Gladstone Commercial Advisers, Inc. [Member] |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |
Company ownership percentage of voting securities of Commercial Advisers (as percent) | 100.00% |  |
GCLP Business Trust I [Member] |  |  |
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 |  |
GCLP Business Trust II [Member] |  |  |
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) | 1.00% |  |
Number of trust shares exchanged for general partnership interest (in shares) | shares | 100 |  |

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