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Real Estate and Intangible Assets - Summary of Total Revenue and Loss Recognized from Business Combination (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2016 | Sep. 30, 2016
Real Estate [Abstract] |  |
Rental Revenue | $ 464 | $ 603
(Loss) | $ (82) | $ (203)

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- Definition Net income loss from acquired properties. + References No definition available. + Details
Name: | good_NetIncomeLossFromAcquiredProperties
Namespace Prefix: | good_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Operating leases income statement lease revenue from acquired properties. + References No definition available. + Details
Name: | good_OperatingLeasesIncomeStatementLeaseRevenueFromAcquiredProperties
Namespace Prefix: | good_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_RealEstateAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration