Quarterly report pursuant to Section 13 or 15(d)

Real Estate and Intangible Assets - Additional Information (Detail)

v2.4.1.9
Real Estate and Intangible Assets - Additional Information (Detail) (USD $)
0 Months Ended 3 Months Ended 0 Months Ended
Feb. 27, 2015
Feb. 20, 2015
Mar. 31, 2015
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Mar. 31, 2014
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Feb. 09, 2015
Option
Property
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Jan. 29, 2015
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Jul. 25, 2014
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Real Estate Properties [Line Items]              
Area of real estate properties     186,834good_AreaOfRealEstateProperties 41,509good_AreaOfRealEstateProperties      
Previously occupied space             81,371us-gaap_AreaOfRealEstateProperty
Lease commission paid     $ 65,000us-gaap_PaymentsForLeaseCommissions $ 54,000us-gaap_PaymentsForLeaseCommissions      
Proceeds from sale of property   2,800,000us-gaap_ProceedsFromSaleOfRealEstate          
Carrying value of property   2,400,000us-gaap_RealEstateGrossAtCarryingValue          
Early termination penalty 1,000,000good_LeaseTerminationFees            
Effective termination date     Dec. 31, 2017        
Lease termination description     Termination option, which allows the tenant to terminate their lease effective December 31, 2017, upon paying a termination penalty of approximately $1.0 million on or before March 31, 2017. All other terms and conditions of the lease remain in full force and effect.        
Indianapolis, Indiana [Member]              
Real Estate Properties [Line Items]              
Number of lease agreements modified   2good_NumberOfLeaseAgreementsModified
/ invest_InvestmentGeographicRegionAxis
= good_IndianapolisMember
         
Raleigh, North Carolina [Member]              
Real Estate Properties [Line Items]              
Extended lease expiration         2020-07    
Amount paid for tenant Improvements         100,000us-gaap_PaymentsForTenantImprovements
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
   
Number of properties expanded         2good_NumberOfPropertiesExpanded
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
   
Number of properties occupied by tenant         2good_NumberOfPropertiesOccupied
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
   
Renew the lease for additional periods         5 years    
Previously occupied space         174,426us-gaap_AreaOfRealEstateProperty
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
   
Reduced space by tenant         94,200good_ReducedLeaseAgreementAreaOccupied
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
   
Annualized straight line rent escalations         900,000us-gaap_StraightLineRentAdjustments
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
   
Lease commission paid         200,000us-gaap_PaymentsForLeaseCommissions
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
   
Number of options for renewal of lease         2good_NumberOfOptionsForRenewalOfLease
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
   
Number of years under additional periods for lease renewal option         5 years    
Raleigh, North Carolina [Member] | Previously Reported [Member]              
Real Estate Properties [Line Items]              
Annualized straight line rent escalations         1,300,000us-gaap_StraightLineRentAdjustments
/ invest_InvestmentGeographicRegionAxis
= good_RaleighNorthCarolinaMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioPreviouslyReportedMember
   
Raleigh, North Carolina [Member] | Lease One [Member]              
Real Estate Properties [Line Items]              
Original lease expiration         2015-07    
Raleigh, North Carolina [Member] | Lease Two [Member]              
Real Estate Properties [Line Items]              
Original lease expiration         2015-07    
Tenant One [Member] | Indianapolis, Indiana [Member]              
Real Estate Properties [Line Items]              
Area of real estate properties           3,546good_AreaOfRealEstateProperties
/ invest_InvestmentGeographicRegionAxis
= good_IndianapolisMember
/ us-gaap_MajorPropertyClassAxis
= good_TenantOneMember
 
Option to extend lease term           7 years  
Extended lease expiration           2023-03  
Original lease expiration           2016-02  
Amount of annualized straight line rents over the life of the lease           60,000us-gaap_OperatingLeasesIncomeStatementMinimumLeaseRevenue
/ invest_InvestmentGeographicRegionAxis
= good_IndianapolisMember
/ us-gaap_MajorPropertyClassAxis
= good_TenantOneMember
 
Amount paid for tenant Improvements           60,000us-gaap_PaymentsForTenantImprovements
/ invest_InvestmentGeographicRegionAxis
= good_IndianapolisMember
/ us-gaap_MajorPropertyClassAxis
= good_TenantOneMember
 
Tenant Two [Member] | Indianapolis, Indiana [Member]              
Real Estate Properties [Line Items]              
Area of real estate properties           7,639good_AreaOfRealEstateProperties
/ invest_InvestmentGeographicRegionAxis
= good_IndianapolisMember
/ us-gaap_MajorPropertyClassAxis
= good_TenantTwoMember
 
Original lease expiration           2018-01  
Amount of annualized straight line rents over the life of the lease           $ 100,000us-gaap_OperatingLeasesIncomeStatementMinimumLeaseRevenue
/ invest_InvestmentGeographicRegionAxis
= good_IndianapolisMember
/ us-gaap_MajorPropertyClassAxis
= good_TenantTwoMember
 
Extended area of real estate property leased           8,275good_ExtendedAreaOfRealEstatePropertyLeased
/ invest_InvestmentGeographicRegionAxis
= good_IndianapolisMember
/ us-gaap_MajorPropertyClassAxis
= good_TenantTwoMember