Annual report pursuant to Section 13 and 15(d)

Mortgage Notes Payable and Line of Credit - Additional Information (Detail)

v2.4.1.9
Mortgage Notes Payable and Line of Credit - Additional Information (Detail) (USD $)
 0 Months Ended 1 Months Ended 3 Months Ended 12 Months Ended
Nov. 12, 2014
Mar. 31, 2014
Aug. 31, 2013
Dec. 31, 2014
Mortgages
Property
Dec. 31, 2014
Mortgages
Property
Nov. 30, 2014
Dec. 31, 2013
Feb. 18, 2015
Debt Instrument [Line Items]                
Number of mortgage notes payable       41good_NumberOfMortgageNotesPayable 41good_NumberOfMortgageNotesPayable      
Weighted average interest on debt outstanding       5.11%us-gaap_DebtWeightedAverageInterestRate 5.11%us-gaap_DebtWeightedAverageInterestRate      
Number of properties collateralized in mortgage notes payable       77good_NumberOfPropertyCollateralizedInMortgageNotesPayable 77good_NumberOfPropertyCollateralizedInMortgageNotesPayable      
Net book value of collateralized mortgage properties       $ 642,500,000us-gaap_MortgageLoansOnRealEstateFaceAmountOfMortgages $ 642,500,000us-gaap_MortgageLoansOnRealEstateFaceAmountOfMortgages      
Number of long-term mortgages issued         2good_NumberOfLongTermMortgagesIssued      
Number of properties to collateralized mortgage notes payable         3good_NumberOfPropertiesToCollateralizedMortgageNotesPayable      
Number of long-term mortgages assumed         4good_NumberOfLongTermMortgagesAssumed      
Number of properties to issue collateralized mortgage notes payable         5good_NumberOfPropertiesIssuedToCollateralizedMortgageNotesPayable      
Carrying value of the property while deed-in-lieu transaction 9,800,000good_CarryingValueOfIndustrialPropertiesCollateralizingMortgage              
Debt outstanding and net reserves held by lender 14,100,000good_DebtOutstandingAndNetReservesHeldByLender              
Gain on debt extinguishment 5,300,000us-gaap_GainsLossesOnExtinguishmentOfDebt     5,300,000us-gaap_GainsLossesOnExtinguishmentOfDebt 5,274,000us-gaap_GainsLossesOnExtinguishmentOfDebt      
Fair value of mortgage notes payable outstanding       476,900,000us-gaap_NotesPayableFairValueDisclosure 476,900,000us-gaap_NotesPayableFairValueDisclosure      
Line of credit, outstanding     60,000,000us-gaap_LineOfCredit 43,300,000us-gaap_LineOfCredit 43,300,000us-gaap_LineOfCredit   24,400,000us-gaap_LineOfCredit  
Line of credit facility, maximum additional amount drawn     100,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity     75,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity    
Line of credit, maturity date   2017-08 2016-08          
Extension period subject to payment of fee   1 year 1 year          
Extension fee on the initial maturity date   0.25%good_LineOfCreditFacilityPercentageOfExtensionFeeOnInitialMaturity 0.25%good_LineOfCreditFacilityPercentageOfExtensionFeeOnInitialMaturity          
Increase in line of credit facility     1,300,000us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet          
Standby letters of credit sublimit     20,000,000good_StandbyLettersOfCreditSublimit          
Line of credit, variable spread on interest rate     3.25%us-gaap_LineOfCreditFacilityInterestRateDuringPeriod          
Annual maintenance fee     30,000good_LineOfCreditFacilityAnnualMaintenanceFee          
Unused commitment fee     0.25%us-gaap_LineOfCreditFacilityCommitmentFeePercentage          
Line of credit covenant limit of distributions to shareholders percentage     100.00%good_LineOfCreditCovenantLimitOfDistributionsToShareholdersPercentage          
Line of credit at an interest rate       3.17%us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd 3.17%us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd      
Subsequent Event [Member]                
Debt Instrument [Line Items]                
Line of credit facility, maximum additional amount drawn               28,300,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Mortgage Notes Payable [Member]                
Debt Instrument [Line Items]                
Weighted average interest on debt outstanding       5.30%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= good_MortgageNotesPayableMember 		5.30%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= good_MortgageNotesPayableMember 		     
Excess of LIBOR rate         3.00%good_DebtInstrumentBaseRate
/ us-gaap_DebtInstrumentAxis
= good_MortgageNotesPayableMember 		     
Carrying value of mortgage notes payable outstanding       458,592,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= good_MortgageNotesPayableMember 		458,592,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= good_MortgageNotesPayableMember 		  421,878,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= good_MortgageNotesPayableMember 		 
Letter of Credit [Member]                
Debt Instrument [Line Items]                
Weighted average interest on debt outstanding       3.00%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_CreditFacilityAxis
= us-gaap_LetterOfCreditMember 		3.00%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_CreditFacilityAxis
= us-gaap_LetterOfCreditMember 		     
Letters of credit, outstanding       $ 4,500,000us-gaap_LettersOfCreditOutstandingAmount
/ us-gaap_CreditFacilityAxis
= us-gaap_LetterOfCreditMember 		$ 4,500,000us-gaap_LettersOfCreditOutstandingAmount
/ us-gaap_CreditFacilityAxis
= us-gaap_LetterOfCreditMember