Annual report pursuant to Section 13 and 15(d)

Real Estate and Intangible Assets - Fair Value of Acquired Assets and Liabilities Assumed (Detail)

v2.4.1.9
Real Estate and Intangible Assets - Fair Value of Acquired Assets and Liabilities Assumed (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Business Acquisition [Line Items]    
Total Purchase Price $ 134,461good_PurchasePriceOfAcquiredProperty $ 131,188good_PurchasePriceOfAcquiredProperty
Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 8,386us-gaap_FairValueOfAssetsAcquired
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
9,069us-gaap_FairValueOfAssetsAcquired
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
Above Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 387us-gaap_FairValueOfAssetsAcquired
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_AboveMarketLeasesMember
336us-gaap_FairValueOfAssetsAcquired
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_AboveMarketLeasesMember
Below Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired (1,236)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_BelowMarketLeaseMember
(1,224)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_BelowMarketLeaseMember
Discount on Assumed Debt [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired (249)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_DiscountPremiumOnAssumedDebtMember
 
Egg Harbor Township, NJ [Member]    
Business Acquisition [Line Items]    
Total Purchase Price   5,650good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_EggHarborTownshipNjMember
Egg Harbor Township, NJ [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   259us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EggHarborTownshipNjMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
Vance, AL [Member]    
Business Acquisition [Line Items]    
Total Purchase Price   13,388good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_VanceAlMember
Vance, AL [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   627us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_VanceAlMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
Blaine, MN [Member]    
Business Acquisition [Line Items]    
Total Purchase Price   14,450good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_BlaineMnMember
Blaine, MN [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   816us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_BlaineMnMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
Austin, Texas [Member]    
Business Acquisition [Line Items]    
Total Purchase Price   57,000good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_AustinTxMember
Austin, Texas [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   3,793us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AustinTxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
Austin, Texas [Member] | Below Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   (1,168)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AustinTxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_BelowMarketLeaseMember
Allen, TX [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 5,525good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
15,150good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
Allen, TX [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 218us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
1,499us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
Allen, TX [Member] | Above Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   336us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_AboveMarketLeasesMember
Allen, TX [Member] | Discount on Assumed Debt [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired (72)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_DiscountPremiumOnAssumedDebtMember
 
Englewood, CO [Member]    
Business Acquisition [Line Items]    
Total Purchase Price   18,250good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_EnglewoodCoMember
Englewood, CO [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,850us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EnglewoodCoMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
Englewood, CO [Member] | Below Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   (56)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EnglewoodCoMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_BelowMarketLeaseMember
Novi, MI [Member]    
Business Acquisition [Line Items]    
Total Purchase Price   7,300good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_NoviMiMember
Novi, MI [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   225us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_NoviMiMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
Colleyville, TX [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 4,523good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
 
Colleyville, TX [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 181us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Colleyville, TX [Member] | Below Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired (6)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_BelowMarketLeaseMember
 
Colleyville, TX [Member] | Discount on Assumed Debt [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired (59)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_DiscountPremiumOnAssumedDebtMember
 
Rancho Cordova, CA [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 8,225good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_RanchoCordovaCaliforniaMember
 
Rancho Cordova, CA [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 278us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_RanchoCordovaCaliforniaMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Coppell, TX [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 5,838good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_CoppelltxMember
 
Coppell, TX [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 230us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_CoppelltxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Coppell, TX [Member] | Discount on Assumed Debt [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired (118)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_CoppelltxMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_DiscountPremiumOnAssumedDebtMember
 
Columbus, OH [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 11,800good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_ColumbusOHMember
 
Columbus, OH [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 990us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColumbusOHMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Columbus, OH [Member] | Above Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 261us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColumbusOHMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_AboveMarketLeasesMember
 
Taylor, PA [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 39,000good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_TaylorpaMember
 
Taylor, PA [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 2,870us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_TaylorpaMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Aurora, CO [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 8,300good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_AuroraMember
 
Aurora, CO [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 282us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AuroraMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Indianapolis, IN [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 10,500good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
 
Indianapolis, IN [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 732us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Indianapolis, IN [Member] | Above Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 126us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_AboveMarketLeasesMember
 
Indianapolis, IN [Member] | Below Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired (13)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_BelowMarketLeaseMember
 
Denver, CO [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 10,000good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_DenverCoMember
 
Denver, CO [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 652us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_DenverCoMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Denver, CO [Member] | Below Market Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired (1,217)us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_DenverCoMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= good_BelowMarketLeaseMember
 
Monroe, MI [Member]    
Business Acquisition [Line Items]    
Total Purchase Price 30,750good_PurchasePriceOfAcquiredProperty
/ us-gaap_BusinessAcquisitionAxis
= good_MonroeMember
 
Monroe, MI [Member] | Customer Relationships [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,953us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_MonroeMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CustomerRelationshipsMember
 
Land [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 14,566us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
10,028us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
Land [Member] | Egg Harbor Township, NJ [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,627us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EggHarborTownshipNjMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
Land [Member] | Vance, AL [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   457us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_VanceAlMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
Land [Member] | Blaine, MN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,060us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_BlaineMnMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
Land [Member] | Austin, Texas [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   2,330us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AustinTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
Land [Member] | Allen, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 874us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
2,699us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
Land [Member] | Englewood, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,503us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EnglewoodCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
Land [Member] | Novi, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   352us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_NoviMiMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
Land [Member] | Colleyville, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,277us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Land [Member] | Rancho Cordova, CA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 752us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_RanchoCordovaCaliforniaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Land [Member] | Coppell, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,448us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_CoppelltxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Land [Member] | Columbus, OH [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 990us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColumbusOHMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Land [Member] | Taylor, PA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 3,102us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_TaylorpaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Land [Member] | Aurora, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 2,882us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AuroraMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Land [Member] | Indianapolis, IN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 502us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Land [Member] | Denver, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,621us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_DenverCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Land [Member] | Monroe, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,118us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_MonroeMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Building [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 85,016us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
80,011us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
Building [Member] | Egg Harbor Township, NJ [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   2,735us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EggHarborTownshipNjMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
Building [Member] | Vance, AL [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   9,721us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_VanceAlMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
Building [Member] | Blaine, MN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   9,347us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_BlaineMnMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
Building [Member] | Austin, Texas [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   37,207us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AustinTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
Building [Member] | Allen, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 3,509us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
5,758us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
Building [Member] | Englewood, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   9,889us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EnglewoodCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
Building [Member] | Novi, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   5,354us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_NoviMiMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
Building [Member] | Colleyville, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 2,307us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Building [Member] | Rancho Cordova, CA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 5,898us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_RanchoCordovaCaliforniaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Building [Member] | Coppell, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 3,221us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_CoppelltxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Building [Member] | Columbus, OH [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 6,080us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColumbusOHMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Building [Member] | Taylor, PA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 24,449us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_TaylorpaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Building [Member] | Aurora, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 3,825us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AuroraMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Building [Member] | Indianapolis, IN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 5,334us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Building [Member] | Denver, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 6,503us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_DenverCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Building [Member] | Monroe, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 23,890us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_MonroeMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Tenant Improvements [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 6,231us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
13,385us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
Tenant Improvements [Member] | Egg Harbor Township, NJ [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   282us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EggHarborTownshipNjMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
Tenant Improvements [Member] | Vance, AL [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   808us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_VanceAlMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
Tenant Improvements [Member] | Blaine, MN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,172us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_BlaineMnMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
Tenant Improvements [Member] | Austin, Texas [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   6,814us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AustinTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
Tenant Improvements [Member] | Allen, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 125us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
2,187us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
Tenant Improvements [Member] | Englewood, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,850us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EnglewoodCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
Tenant Improvements [Member] | Novi, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   272us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_NoviMiMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
Tenant Improvements [Member] | Colleyville, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 117us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
Tenant Improvements [Member] | Rancho Cordova, CA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 278us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_RanchoCordovaCaliforniaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
Tenant Improvements [Member] | Coppell, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 128us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_CoppelltxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
Tenant Improvements [Member] | Columbus, OH [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,937us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColumbusOHMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
Tenant Improvements [Member] | Taylor, PA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 956us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_TaylorpaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
Tenant Improvements [Member] | Aurora, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 92us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AuroraMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
Tenant Improvements [Member] | Indianapolis, IN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,088us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
Tenant Improvements [Member] | Denver, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 568us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_DenverCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
Tenant Improvements [Member] | Monroe, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 942us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_MonroeMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_TenantImprovementMember
 
In-Place Leases [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 14,239us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
13,358us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
In-Place Leases [Member] | Egg Harbor Township, NJ [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   558us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EggHarborTownshipNjMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
In-Place Leases [Member] | Vance, AL [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,097us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_VanceAlMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
In-Place Leases [Member] | Blaine, MN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,361us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_BlaineMnMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
In-Place Leases [Member] | Austin, Texas [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   6,118us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AustinTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
In-Place Leases [Member] | Allen, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 598us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
1,525us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
In-Place Leases [Member] | Englewood, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   2,036us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EnglewoodCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
In-Place Leases [Member] | Novi, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   663us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_NoviMiMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
In-Place Leases [Member] | Colleyville, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 486us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
In-Place Leases [Member] | Rancho Cordova, CA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 473us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_RanchoCordovaCaliforniaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
In-Place Leases [Member] | Coppell, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 636us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_CoppelltxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
In-Place Leases [Member] | Columbus, OH [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 823us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColumbusOHMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
In-Place Leases [Member] | Taylor, PA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 6,171us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_TaylorpaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
In-Place Leases [Member] | Aurora, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 413us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AuroraMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
In-Place Leases [Member] | Indianapolis, IN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,990us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
In-Place Leases [Member] | Denver, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,152us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_DenverCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
In-Place Leases [Member] | Monroe, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,497us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_MonroeMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_InPlaceLeasesMember
 
Leasing Costs [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 7,121us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
6,225us-gaap_FairValueOfAssetsAcquired
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
Leasing Costs [Member] | Egg Harbor Township, NJ [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   189us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EggHarborTownshipNjMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
Leasing Costs [Member] | Vance, AL [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   678us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_VanceAlMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
Leasing Costs [Member] | Blaine, MN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   694us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_BlaineMnMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
Leasing Costs [Member] | Austin, Texas [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,906us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AustinTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
Leasing Costs [Member] | Allen, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 273us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
1,146us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
Leasing Costs [Member] | Englewood, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   1,178us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_EnglewoodCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
Leasing Costs [Member] | Novi, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired   434us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_NoviMiMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
Leasing Costs [Member] | Colleyville, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 220us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilletxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
 
Leasing Costs [Member] | Rancho Cordova, CA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 546us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_RanchoCordovaCaliforniaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
 
Leasing Costs [Member] | Coppell, TX [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 293us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_CoppelltxMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
 
Leasing Costs [Member] | Columbus, OH [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 719us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_ColumbusOHMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
 
Leasing Costs [Member] | Taylor, PA [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 1,452us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_TaylorpaMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
 
Leasing Costs [Member] | Aurora, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 806us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_AuroraMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
 
Leasing Costs [Member] | Indianapolis, IN [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 741us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_IndianapolisMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
 
Leasing Costs [Member] | Denver, CO [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired 721us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_DenverCoMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember
 
Leasing Costs [Member] | Monroe, MI [Member]    
Business Acquisition [Line Items]    
Fair value of acquired assets related to the properties acquired $ 1,350us-gaap_FairValueOfAssetsAcquired
/ us-gaap_BusinessAcquisitionAxis
= good_MonroeMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= good_LeasingCostsMember