XML 54 R39.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Real Estate and Intangible Assets - Schedule of Revenue and Earnings Recognized on Properties Acquired (Detail) - Asset Acquisitions [Member] $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2016 USD ($) acquisition | Dec. 31, 2015 USD ($) acquisition | Dec. 31, 2014 USD ($) acquisition
Business Acquisition [Line Items] |  |  |
Number Of Acquisitions Completed | acquisition | 2 | 6 | 11
Rental Revenue | $ 1,462 | $ 4,919 | $ 5,605
Earnings | $ (162) | $ (63) | $ 36

X
- 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

X
- Definition Number of acquisitions completed. + References No definition available. + Details
Name: | good_NumberOfAcquisitionsCompleted
Namespace Prefix: | good_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- 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

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=good_AssetAcquisitionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |