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    <link:label id="lab_us-gaap_MortgagesMember_5809956F2275FBE12D2A3DDB9C324702_terseLabel_en-US" xlink:label="lab_us-gaap_MortgagesMember_5809956F2275FBE12D2A3DDB9C324702" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Mortgages</link:label>
    <link:label id="lab_us-gaap_MortgagesMember_5809956F2275FBE12D2A3DDB9C324702_label_en-US" xlink:label="lab_us-gaap_MortgagesMember_5809956F2275FBE12D2A3DDB9C324702" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Mortgages [Member]</link:label>
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    <link:label id="lab_good_NewFixedRateMortgageNotesPayableMember_7B6D4E45AF1128D1729A3DDB9C39FB09_terseLabel_en-US" xlink:label="lab_good_NewFixedRateMortgageNotesPayableMember_7B6D4E45AF1128D1729A3DDB9C39FB09" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">New fixed rate mortgage notes payable</link:label>
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    <link:label id="lab_good_VariableRateMortgageLoansDebtExtendedMember_4C1C05BC0C14412BF4D03DDB9C39F927_terseLabel_en-US" xlink:label="lab_good_VariableRateMortgageLoansDebtExtendedMember_4C1C05BC0C14412BF4D03DDB9C39F927" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Variable rate mortgage loans debt extended</link:label>
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    <link:loc xlink:href="good-20190630.xsd#good_VariableRateMortgageLoansDebtExtendedMember" xlink:label="loc_good_VariableRateMortgageLoansDebtExtendedMember_4C1C05BC0C14412BF4D03DDB9C39F927" xlink:type="locator" />
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    <link:loc xlink:href="good-20190630.xsd#good_MortgageNotesPayableMember" xlink:label="loc_good_MortgageNotesPayableMember_10A745699E1A6C8C834A3DDB9C3A6585" xlink:type="locator" />
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    <link:label id="lab_us-gaap_UsTreasuryUstInterestRateMember_07D2EDAB0093FD9FA6813DF5E11BBED5_label_en-US" xlink:label="lab_us-gaap_UsTreasuryUstInterestRateMember_07D2EDAB0093FD9FA6813DF5E11BBED5" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">US Treasury (UST) Interest Rate [Member]</link:label>
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    <link:label id="lab_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_BBDE25DB6CA5F00EDE633DDB9C3C7E17_terseLabel_en-US" xlink:label="lab_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_BBDE25DB6CA5F00EDE633DDB9C3C7E17" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Name of Property [Axis]</link:label>
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    <link:label id="lab_good_PropertyMaturingFebruary82029Member_C78F195F5195D3ED46563DDB9C3CC247_terseLabel_en-US" xlink:label="lab_good_PropertyMaturingFebruary82029Member_C78F195F5195D3ED46563DDB9C3CC247" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Property maturing February 8, 2029</link:label>
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    <link:label id="lab_good_PropertyMaturingJune182024Member_01A0EEC589798554719B3DDB9C3D2138_terseLabel_en-US" xlink:label="lab_good_PropertyMaturingJune182024Member_01A0EEC589798554719B3DDB9C3D2138" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Property maturing June 18, 2024</link:label>
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    <link:label id="lab_srt_MortgageLoansOnRealEstateFaceAmountOfMortgages_D01269B8B0310F52211F3F7E17C15B8D_terseLabel_en-US" xlink:label="lab_srt_MortgageLoansOnRealEstateFaceAmountOfMortgages_D01269B8B0310F52211F3F7E17C15B8D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Net book value of collateralized mortgage properties</link:label>
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    <link:label id="lab_us-gaap_AreaOfRealEstateProperty_104A5CE0A01B1BA2F9A98B26A5C21B4E_terseLabel_en-US" xlink:label="lab_us-gaap_AreaOfRealEstateProperty_104A5CE0A01B1BA2F9A98B26A5C21B4E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Square Footage Sold</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AreaOfRealEstateProperty" xlink:label="loc_us-gaap_AreaOfRealEstateProperty_104A5CE0A01B1BA2F9A98B26A5C21B4E" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AreaOfRealEstateProperty_104A5CE0A01B1BA2F9A98B26A5C21B4E" xlink:to="lab_us-gaap_AreaOfRealEstateProperty_104A5CE0A01B1BA2F9A98B26A5C21B4E" xlink:type="arc" />
    <link:label id="lab_us-gaap_ProceedsFromSaleOfPropertyHeldForSale_C2BBB63A70B43CF25C3C8B26A5C341D2_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfPropertyHeldForSale_C2BBB63A70B43CF25C3C8B26A5C341D2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Sales Price</link:label>
    <link:label id="lab_us-gaap_ProceedsFromSaleOfPropertyHeldForSale_C2BBB63A70B43CF25C3C8B26A5C341D2_label_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfPropertyHeldForSale_C2BBB63A70B43CF25C3C8B26A5C341D2" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Proceeds from Sale of Property Held-for-sale</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromSaleOfPropertyHeldForSale" xlink:label="loc_us-gaap_ProceedsFromSaleOfPropertyHeldForSale_C2BBB63A70B43CF25C3C8B26A5C341D2" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ProceedsFromSaleOfPropertyHeldForSale_C2BBB63A70B43CF25C3C8B26A5C341D2" xlink:to="lab_us-gaap_ProceedsFromSaleOfPropertyHeldForSale_C2BBB63A70B43CF25C3C8B26A5C341D2" xlink:type="arc" />
    <link:label id="lab_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A_terseLabel_en-US" xlink:label="lab_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Sales Costs</link:label>
    <link:label id="lab_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A_label_en-US" xlink:label="lab_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Property Held-for-sale, Selling Costs</link:label>
    <link:label id="lab_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A_documentation_en-US" xlink:label="lab_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Property Held-for-sale, Selling Costs</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_PropertyHeldforsaleSellingCosts" xlink:label="loc_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A" xlink:to="lab_good_PropertyHeldforsaleSellingCosts_F94C02EAE6AD3CC4083C8B26A5C3DF5A" xlink:type="arc" />
    <link:label id="lab_us-gaap_GainLossOnSaleOfProperties_93DAD707F7C234584A7F8B26A5C32970_verboseLabel_en-US" xlink:label="lab_us-gaap_GainLossOnSaleOfProperties_93DAD707F7C234584A7F8B26A5C32970" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xml:lang="en-US">Gain on Sale of Real Estate, net</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GainLossOnSaleOfProperties" xlink:label="loc_us-gaap_GainLossOnSaleOfProperties_93DAD707F7C234584A7F8B26A5C32970" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GainLossOnSaleOfProperties_93DAD707F7C234584A7F8B26A5C32970" xlink:to="lab_us-gaap_GainLossOnSaleOfProperties_93DAD707F7C234584A7F8B26A5C32970" xlink:type="arc" />
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_2F2499C80243320DB8C03E0D52F33B31_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_2F2499C80243320DB8C03E0D52F33B31" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Six Months Ending 2019</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_2F2499C80243320DB8C03E0D52F33B31_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_2F2499C80243320DB8C03E0D52F33B31" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_2F2499C80243320DB8C03E0D52F33B31" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_2F2499C80243320DB8C03E0D52F33B31" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_2F2499C80243320DB8C03E0D52F33B31" xlink:type="arc" />
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_25A902A97FF0B1EC7BBD3E0E13840256_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_25A902A97FF0B1EC7BBD3E0E13840256" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2020</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_25A902A97FF0B1EC7BBD3E0E13840256_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_25A902A97FF0B1EC7BBD3E0E13840256" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received, Two Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_25A902A97FF0B1EC7BBD3E0E13840256" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_25A902A97FF0B1EC7BBD3E0E13840256" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_25A902A97FF0B1EC7BBD3E0E13840256" xlink:type="arc" />
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_0458DC790C2A22F634993E0EA60F3E95_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_0458DC790C2A22F634993E0EA60F3E95" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2021</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_0458DC790C2A22F634993E0EA60F3E95_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_0458DC790C2A22F634993E0EA60F3E95" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received, Three Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_0458DC790C2A22F634993E0EA60F3E95" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_0458DC790C2A22F634993E0EA60F3E95" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_0458DC790C2A22F634993E0EA60F3E95" xlink:type="arc" />
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_6CD0CD66D89D3BFEF18D3E0F2E443D73_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_6CD0CD66D89D3BFEF18D3E0F2E443D73" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2022</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_6CD0CD66D89D3BFEF18D3E0F2E443D73_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_6CD0CD66D89D3BFEF18D3E0F2E443D73" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received, Four Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_6CD0CD66D89D3BFEF18D3E0F2E443D73" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_6CD0CD66D89D3BFEF18D3E0F2E443D73" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_6CD0CD66D89D3BFEF18D3E0F2E443D73" xlink:type="arc" />
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFiveYears_4BFDF814C98BCF6274003E0FD319C798_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFiveYears_4BFDF814C98BCF6274003E0FD319C798" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2023</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFiveYears_4BFDF814C98BCF6274003E0FD319C798_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFiveYears_4BFDF814C98BCF6274003E0FD319C798" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received, Five Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedFiveYears" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFiveYears_4BFDF814C98BCF6274003E0FD319C798" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFiveYears_4BFDF814C98BCF6274003E0FD319C798" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFiveYears_4BFDF814C98BCF6274003E0FD319C798" xlink:type="arc" />
    <link:label id="lab_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC_terseLabel_en-US" xlink:label="lab_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2024</link:label>
    <link:label id="lab_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC_label_en-US" xlink:label="lab_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received, Six Years</link:label>
    <link:label id="lab_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC_documentation_en-US" xlink:label="lab_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received, Six Years</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_LessorOperatingLeasePaymentstobeReceivedSixYears" xlink:label="loc_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC" xlink:to="lab_good_LessorOperatingLeasePaymentstobeReceivedSixYears_DF3FD7ED04D6D8FED5453E1109A24DBC" xlink:type="arc" />
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_610CC599555F8F3E9ACD3E11580849DB_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_610CC599555F8F3E9ACD3E11580849DB" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Thereafter</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_610CC599555F8F3E9ACD3E11580849DB_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_610CC599555F8F3E9ACD3E11580849DB" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received, Thereafter</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_610CC599555F8F3E9ACD3E11580849DB" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_610CC599555F8F3E9ACD3E11580849DB" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_610CC599555F8F3E9ACD3E11580849DB" xlink:type="arc" />
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived_0C70AEF06FEEBC0924773E11C5F20BFF_totalLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived_0C70AEF06FEEBC0924773E11C5F20BFF" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Tenant Lease Payments</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived_0C70AEF06FEEBC0924773E11C5F20BFF_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived_0C70AEF06FEEBC0924773E11C5F20BFF" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceived" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceived_0C70AEF06FEEBC0924773E11C5F20BFF" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceived_0C70AEF06FEEBC0924773E11C5F20BFF" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived_0C70AEF06FEEBC0924773E11C5F20BFF" xlink:type="arc" />
    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableRemainderOfFiscalYear_9C7C397919CCB9CF084F3E192193544E_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableRemainderOfFiscalYear_9C7C397919CCB9CF084F3E192193544E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2019</link:label>
    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableRemainderOfFiscalYear_9C7C397919CCB9CF084F3E192193544E_label_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableRemainderOfFiscalYear_9C7C397919CCB9CF084F3E192193544E" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Operating Leases, Future Minimum Payments Receivable, Remainder of Fiscal Year</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableRemainderOfFiscalYear" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableRemainderOfFiscalYear_9C7C397919CCB9CF084F3E192193544E" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableRemainderOfFiscalYear_9C7C397919CCB9CF084F3E192193544E" xlink:to="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableRemainderOfFiscalYear_9C7C397919CCB9CF084F3E192193544E" xlink:type="arc" />
    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInTwoYears_C1A22A09FB30790B78F03E1A04FF2752_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInTwoYears_C1A22A09FB30790B78F03E1A04FF2752" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2020</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInTwoYears" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInTwoYears_C1A22A09FB30790B78F03E1A04FF2752" xlink:type="locator" />
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    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_D46ED9D63DB8E9DA4F763DDB9B8FB0A6" xlink:to="lab_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_D46ED9D63DB8E9DA4F763DDB9B8FB0A6" xlink:type="arc" />
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear_14DBA9CA2D89C41F2AA43DDB9B8F7D46_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear_14DBA9CA2D89C41F2AA43DDB9B8F7D46" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Six Months Ending December 31, 2019</link:label>
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_9E9BD3E0F433C34D57F53DDB9B90E128_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_9E9BD3E0F433C34D57F53DDB9B90E128" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2020</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_9E9BD3E0F433C34D57F53DDB9B90E128" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_9E9BD3E0F433C34D57F53DDB9B90E128" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_9E9BD3E0F433C34D57F53DDB9B90E128" xlink:type="arc" />
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_1827AEA3F846BC4D514D3DDB9B9034C5_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_1827AEA3F846BC4D514D3DDB9B9034C5" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2021</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_1827AEA3F846BC4D514D3DDB9B9034C5_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_1827AEA3F846BC4D514D3DDB9B9034C5" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessee, Operating Lease, Liability, Payments, Due Year Three</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_1827AEA3F846BC4D514D3DDB9B9034C5" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_1827AEA3F846BC4D514D3DDB9B9034C5" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_1827AEA3F846BC4D514D3DDB9B9034C5" xlink:type="arc" />
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_1B3FAEC7927709547AD23DDB9B904B79_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_1B3FAEC7927709547AD23DDB9B904B79" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2022</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_1B3FAEC7927709547AD23DDB9B904B79_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_1B3FAEC7927709547AD23DDB9B904B79" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessee, Operating Lease, Liability, Payments, Due Year Four</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_1B3FAEC7927709547AD23DDB9B904B79" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_A6938B664582ADD491213DDB9B90B5EA_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_A6938B664582ADD491213DDB9B90B5EA" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2023</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_A6938B664582ADD491213DDB9B90B5EA_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_A6938B664582ADD491213DDB9B90B5EA" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessee, Operating Lease, Liability, Payments, Due Year Five</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_A6938B664582ADD491213DDB9B90B5EA" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_A6938B664582ADD491213DDB9B90B5EA" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_A6938B664582ADD491213DDB9B90B5EA" xlink:type="arc" />
    <link:label id="lab_good_LesseeOperatingLeaseLiabilityPaymentsDueYearSix_BA4B699E6B67410A4BD43DDB9B91B8A0_terseLabel_en-US" xlink:label="lab_good_LesseeOperatingLeaseLiabilityPaymentsDueYearSix_BA4B699E6B67410A4BD43DDB9B91B8A0" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2024</link:label>
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    <link:label id="lab_good_LesseeOperatingLeaseLiabilityPaymentsDueYearSix_BA4B699E6B67410A4BD43DDB9B91B8A0_documentation_en-US" xlink:label="lab_good_LesseeOperatingLeaseLiabilityPaymentsDueYearSix_BA4B699E6B67410A4BD43DDB9B91B8A0" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Lessee, Operating Lease, Liability, Payments, Due Year Six</link:label>
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    <link:label id="lab_good_LesseeOperatingLeaseLiabilityPaymentsDueafterYearSix_93E932470B37450952443DDB9B9101D0_terseLabel_en-US" xlink:label="lab_good_LesseeOperatingLeaseLiabilityPaymentsDueafterYearSix_93E932470B37450952443DDB9B9101D0" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Thereafter</link:label>
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_3F55647BE3D3F0381C6F3DDB9B911039_totalLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_3F55647BE3D3F0381C6F3DDB9B911039" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Total anticipated lease payments</link:label>
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_A5D8DA323294067E22C23DDB9B918690_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_A5D8DA323294067E22C23DDB9B918690" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xml:lang="en-US">Less: amount representing interest</link:label>
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    <link:label id="lab_good_IncentiveFeeWaived_754FDCCFD43AB9A0220229A7B7661E0D_terseLabel_en-US" xlink:label="lab_good_IncentiveFeeWaived_754FDCCFD43AB9A0220229A7B7661E0D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Portion of incentive fee waived</link:label>
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    <link:label id="lab_good_PercentageOfIncentiveFeesOnCapitalGains_E69AFD370CAB00301DBC29A7B76721A9_terseLabel_en-US" xlink:label="lab_good_PercentageOfIncentiveFeesOnCapitalGains_E69AFD370CAB00301DBC29A7B76721A9" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Capital gains-based incentive fee (as percent)</link:label>
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    <link:label id="lab_good_AreaOfLeasedProperty_800DCFA300787BF458CE2E62C2B4F1F1_terseLabel_en-US" xlink:label="lab_good_AreaOfLeasedProperty_800DCFA300787BF458CE2E62C2B4F1F1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Aggregate Square Footage</link:label>
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    <link:label id="lab_us-gaap_AmortizationOfDebtDiscountPremium_8042807DF265CADF250B2F789E2CEC07_terseLabel_en-US" xlink:label="lab_us-gaap_AmortizationOfDebtDiscountPremium_8042807DF265CADF250B2F789E2CEC07" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Amortization of discount and premium on assumed debt, net</link:label>
    <link:label id="lab_us-gaap_AmortizationOfDebtDiscountPremium_8042807DF265CADF250B2F789E2CEC07_label_en-US" xlink:label="lab_us-gaap_AmortizationOfDebtDiscountPremium_8042807DF265CADF250B2F789E2CEC07" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Amortization of Debt Discount (Premium)</link:label>
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    <link:label id="lab_good_AssetRetirementObligationExpense_D99A83A307BCAAE21F8F2F789E2CA553_terseLabel_en-US" xlink:label="lab_good_AssetRetirementObligationExpense_D99A83A307BCAAE21F8F2F789E2CA553" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Asset retirement obligation expense</link:label>
    <link:label id="lab_good_AssetRetirementObligationExpense_D99A83A307BCAAE21F8F2F789E2CA553_label_en-US" xlink:label="lab_good_AssetRetirementObligationExpense_D99A83A307BCAAE21F8F2F789E2CA553" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Asset Retirement Obligation Expense</link:label>
    <link:label id="lab_good_AssetRetirementObligationExpense_D99A83A307BCAAE21F8F2F789E2CA553_documentation_en-US" xlink:label="lab_good_AssetRetirementObligationExpense_D99A83A307BCAAE21F8F2F789E2CA553" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Asset retirement obligation expense.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_AssetRetirementObligationExpense" xlink:label="loc_good_AssetRetirementObligationExpense_D99A83A307BCAAE21F8F2F789E2CA553" xlink:type="locator" />
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    <link:label id="lab_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_04BA9ACDBAA7FF8ED07E2F789E2CACD6_terseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_04BA9ACDBAA7FF8ED07E2F789E2CACD6" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Operating changes in assets and liabilities</link:label>
    <link:label id="lab_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_04BA9ACDBAA7FF8ED07E2F789E2CACD6_label_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_04BA9ACDBAA7FF8ED07E2F789E2CACD6" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Increase (Decrease) in Operating Capital [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_04BA9ACDBAA7FF8ED07E2F789E2CACD6" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_04BA9ACDBAA7FF8ED07E2F789E2CACD6" xlink:to="lab_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_04BA9ACDBAA7FF8ED07E2F789E2CACD6" xlink:type="arc" />
    <link:label id="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets_9E3EEAA6D7BCBA7BB3FF2F789E2D8054_negatedLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets_9E3EEAA6D7BCBA7BB3FF2F789E2D8054" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Increase in other assets</link:label>
    <link:label id="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets_9E3EEAA6D7BCBA7BB3FF2F789E2D8054_label_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets_9E3EEAA6D7BCBA7BB3FF2F789E2D8054" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Increase (Decrease) in Other Operating Assets</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_9E3EEAA6D7BCBA7BB3FF2F789E2D8054" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_9E3EEAA6D7BCBA7BB3FF2F789E2D8054" xlink:to="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets_9E3EEAA6D7BCBA7BB3FF2F789E2D8054" xlink:type="arc" />
    <link:label id="lab_us-gaap_StraightLineRent_6F97676BD868B63FA4A62F789E2DA57A_negatedLabel_en-US" xlink:label="lab_us-gaap_StraightLineRent_6F97676BD868B63FA4A62F789E2DA57A" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Increase in deferred rent receivable</link:label>
    <link:label id="lab_us-gaap_StraightLineRent_6F97676BD868B63FA4A62F789E2DA57A_label_en-US" xlink:label="lab_us-gaap_StraightLineRent_6F97676BD868B63FA4A62F789E2DA57A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Straight Line Rent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StraightLineRent" xlink:label="loc_us-gaap_StraightLineRent_6F97676BD868B63FA4A62F789E2DA57A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StraightLineRent_6F97676BD868B63FA4A62F789E2DA57A" xlink:to="lab_us-gaap_StraightLineRent_6F97676BD868B63FA4A62F789E2DA57A" xlink:type="arc" />
    <link:label id="lab_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_9A75FE125BEC5006ACA22F789E2D0722_terseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_9A75FE125BEC5006ACA22F789E2D0722" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Increase (decrease) in accounts payable, accrued expenses, and amount due to Adviser and Administrator</link:label>
    <link:label id="lab_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_9A75FE125BEC5006ACA22F789E2D0722_label_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_9A75FE125BEC5006ACA22F789E2D0722" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Increase (Decrease) in Accounts Payable and Accrued Liabilities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_9A75FE125BEC5006ACA22F789E2D0722" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_9A75FE125BEC5006ACA22F789E2D0722" xlink:to="lab_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_9A75FE125BEC5006ACA22F789E2D0722" xlink:type="arc" />
    <link:label id="lab_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382_terseLabel_en-US" xlink:label="lab_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Decrease in right-of-use asset from operating leases</link:label>
    <link:label id="lab_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382_label_en-US" xlink:label="lab_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessee, Operating Lease, Amortization of Right-Of-Use Asset</link:label>
    <link:label id="lab_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382_documentation_en-US" xlink:label="lab_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Lessee, Operating Lease, Amortization of Right-Of-Use Asset</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_LesseeOperatingLeaseAmortizationofRightOfUseAsset" xlink:label="loc_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382" xlink:to="lab_good_LesseeOperatingLeaseAmortizationofRightOfUseAsset_D49706B729C5032B18DA2F789E2DF382" xlink:type="arc" />
    <link:label id="lab_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86_negatedTerseLabel_en-US" xlink:label="lab_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xml:lang="en-US">Decrease in operating lease liabilities</link:label>
    <link:label id="lab_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86_label_en-US" xlink:label="lab_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lessee, Operating Lease, Amortization of Lease Liability</link:label>
    <link:label id="lab_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86_documentation_en-US" xlink:label="lab_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Lessee, Operating Lease, Amortization of Lease Liability</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_LesseeOperatingLeaseAmortizationofLeaseLiability" xlink:label="loc_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86" xlink:to="lab_good_LesseeOperatingLeaseAmortizationofLeaseLiability_2859FBBA73559DF4FFA42F789E2DAF86" xlink:type="arc" />
    <link:label id="lab_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3810CEF942106F9471E72F789E2DF81A_terseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3810CEF942106F9471E72F789E2DF81A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Increase (decrease) in other liabilities</link:label>
    <link:label id="lab_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3810CEF942106F9471E72F789E2DF81A_label_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3810CEF942106F9471E72F789E2DF81A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Increase (Decrease) in Other Operating Liabilities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3810CEF942106F9471E72F789E2DF81A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3810CEF942106F9471E72F789E2DF81A" xlink:to="lab_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3810CEF942106F9471E72F789E2DF81A" xlink:type="arc" />
    <link:label id="lab_us-gaap_PaymentsForCommissions_89F3F4DC6AE45EC45F882F789E2EC399_negatedLabel_en-US" xlink:label="lab_us-gaap_PaymentsForCommissions_89F3F4DC6AE45EC45F882F789E2EC399" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Leasing commissions paid</link:label>
    <link:label id="lab_us-gaap_PaymentsForCommissions_89F3F4DC6AE45EC45F882F789E2EC399_label_en-US" xlink:label="lab_us-gaap_PaymentsForCommissions_89F3F4DC6AE45EC45F882F789E2EC399" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Payments for Commissions</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsForCommissions" xlink:label="loc_us-gaap_PaymentsForCommissions_89F3F4DC6AE45EC45F882F789E2EC399" xlink:type="locator" />
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_3F9D0527DC1CC5F3D4702F789E2E754F_totalLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_3F9D0527DC1CC5F3D4702F789E2E754F" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Net cash provided by operating activities</link:label>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_3F9D0527DC1CC5F3D4702F789E2E754F_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_3F9D0527DC1CC5F3D4702F789E2E754F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Net Cash Provided by (Used in) Operating Activities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_3F9D0527DC1CC5F3D4702F789E2E754F" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_3F9D0527DC1CC5F3D4702F789E2E754F" xlink:to="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_3F9D0527DC1CC5F3D4702F789E2E754F" xlink:type="arc" />
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_62CFF42BA791074D54F82F789E2E5205_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_62CFF42BA791074D54F82F789E2E5205" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Cash flows from investing activities:</link:label>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_62CFF42BA791074D54F82F789E2E5205_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_62CFF42BA791074D54F82F789E2E5205" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Net Cash Provided by (Used in) Investing Activities [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_62CFF42BA791074D54F82F789E2E5205" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_62CFF42BA791074D54F82F789E2E5205" xlink:to="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_62CFF42BA791074D54F82F789E2E5205" xlink:type="arc" />
    <link:label id="lab_good_PaymentsToAcquireRealEstateAndIntangibleAssets_FDD93A5193BD021396D32F789E2ECCE4_negatedTerseLabel_en-US" xlink:label="lab_good_PaymentsToAcquireRealEstateAndIntangibleAssets_FDD93A5193BD021396D32F789E2ECCE4" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xml:lang="en-US">Acquisition of real estate and related intangible assets</link:label>
    <link:label id="lab_good_PaymentsToAcquireRealEstateAndIntangibleAssets_FDD93A5193BD021396D32F789E2ECCE4_label_en-US" xlink:label="lab_good_PaymentsToAcquireRealEstateAndIntangibleAssets_FDD93A5193BD021396D32F789E2ECCE4" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Payments To Acquire Real Estate And Intangible Assets</link:label>
    <link:label id="lab_good_PaymentsToAcquireRealEstateAndIntangibleAssets_FDD93A5193BD021396D32F789E2ECCE4_documentation_en-US" xlink:label="lab_good_PaymentsToAcquireRealEstateAndIntangibleAssets_FDD93A5193BD021396D32F789E2ECCE4" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Payments to acquire real estate and intangible assets.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_PaymentsToAcquireRealEstateAndIntangibleAssets" xlink:label="loc_good_PaymentsToAcquireRealEstateAndIntangibleAssets_FDD93A5193BD021396D32F789E2ECCE4" xlink:type="locator" />
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    <link:label id="lab_good_ImprovementsOfExistingRealEstate_782312E1650E4A872B1C2F789E2EBD00_negatedLabel_en-US" xlink:label="lab_good_ImprovementsOfExistingRealEstate_782312E1650E4A872B1C2F789E2EBD00" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Improvements of existing real estate</link:label>
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    <link:label id="lab_good_ImprovementsOfExistingRealEstate_782312E1650E4A872B1C2F789E2EBD00_documentation_en-US" xlink:label="lab_good_ImprovementsOfExistingRealEstate_782312E1650E4A872B1C2F789E2EBD00" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Improvements of existing real estate.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_ImprovementsOfExistingRealEstate" xlink:label="loc_good_ImprovementsOfExistingRealEstate_782312E1650E4A872B1C2F789E2EBD00" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_ImprovementsOfExistingRealEstate_782312E1650E4A872B1C2F789E2EBD00" xlink:to="lab_good_ImprovementsOfExistingRealEstate_782312E1650E4A872B1C2F789E2EBD00" xlink:type="arc" />
    <link:label id="lab_us-gaap_ProceedsFromSaleOfRealEstate_0DC70CD60EE82A3E53DF2F789E2F8031_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfRealEstate_0DC70CD60EE82A3E53DF2F789E2F8031" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Proceeds from sale of real estate</link:label>
    <link:label id="lab_us-gaap_ProceedsFromSaleOfRealEstate_0DC70CD60EE82A3E53DF2F789E2F8031_label_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfRealEstate_0DC70CD60EE82A3E53DF2F789E2F8031" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Proceeds from Sale of Real Estate</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromSaleOfRealEstate" xlink:label="loc_us-gaap_ProceedsFromSaleOfRealEstate_0DC70CD60EE82A3E53DF2F789E2F8031" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ProceedsFromSaleOfRealEstate_0DC70CD60EE82A3E53DF2F789E2F8031" xlink:to="lab_us-gaap_ProceedsFromSaleOfRealEstate_0DC70CD60EE82A3E53DF2F789E2F8031" xlink:type="arc" />
    <link:label id="lab_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A_terseLabel_en-US" xlink:label="lab_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Receipts from lenders for funds held in escrow</link:label>
    <link:label id="lab_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A_label_en-US" xlink:label="lab_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Receipts From Lenders For Reserves Held In Escrow</link:label>
    <link:label id="lab_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A_documentation_en-US" xlink:label="lab_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Receipts from lenders for funds held in escrow.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_ReceiptsFromLendersForReservesHeldInEscrow" xlink:label="loc_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A" xlink:to="lab_good_ReceiptsFromLendersForReservesHeldInEscrow_1C1D7DAAAD5B6E5C66772F789E2F781A" xlink:type="arc" />
    <link:label id="lab_good_PaymentsToLendersForReservesHeldInEscrow_37D34EBD3ACA1FFB1F8D2F789E2FA107_negatedLabel_en-US" xlink:label="lab_good_PaymentsToLendersForReservesHeldInEscrow_37D34EBD3ACA1FFB1F8D2F789E2FA107" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Payments to lenders for funds held in escrow</link:label>
    <link:label id="lab_good_PaymentsToLendersForReservesHeldInEscrow_37D34EBD3ACA1FFB1F8D2F789E2FA107_label_en-US" xlink:label="lab_good_PaymentsToLendersForReservesHeldInEscrow_37D34EBD3ACA1FFB1F8D2F789E2FA107" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Payments To Lenders For Reserves Held In Escrow</link:label>
    <link:label id="lab_good_PaymentsToLendersForReservesHeldInEscrow_37D34EBD3ACA1FFB1F8D2F789E2FA107_documentation_en-US" xlink:label="lab_good_PaymentsToLendersForReservesHeldInEscrow_37D34EBD3ACA1FFB1F8D2F789E2FA107" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Payments to lenders for reserves held in escrow.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_PaymentsToLendersForReservesHeldInEscrow" xlink:label="loc_good_PaymentsToLendersForReservesHeldInEscrow_37D34EBD3ACA1FFB1F8D2F789E2FA107" xlink:type="locator" />
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    <link:label id="lab_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F_terseLabel_en-US" xlink:label="lab_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Receipts from tenants for reserves</link:label>
    <link:label id="lab_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F_label_en-US" xlink:label="lab_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Receipts From Tenants For Reserves</link:label>
    <link:label id="lab_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F_documentation_en-US" xlink:label="lab_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Receipts from tenants for reserves.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_ReceiptsFromTenantsForReserves" xlink:label="loc_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F" xlink:to="lab_good_ReceiptsFromTenantsForReserves_EB159D6750A34C872B602F789E2F072F" xlink:type="arc" />
    <link:label id="lab_good_PaymentsToTenantsFromReserves_23B2E5AAD79EE87C63462F789E2F9FF6_negatedLabel_en-US" xlink:label="lab_good_PaymentsToTenantsFromReserves_23B2E5AAD79EE87C63462F789E2F9FF6" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Payments to tenants from reserves</link:label>
    <link:label id="lab_good_PaymentsToTenantsFromReserves_23B2E5AAD79EE87C63462F789E2F9FF6_label_en-US" xlink:label="lab_good_PaymentsToTenantsFromReserves_23B2E5AAD79EE87C63462F789E2F9FF6" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Payments To Tenants From Reserves</link:label>
    <link:label id="lab_good_PaymentsToTenantsFromReserves_23B2E5AAD79EE87C63462F789E2F9FF6_documentation_en-US" xlink:label="lab_good_PaymentsToTenantsFromReserves_23B2E5AAD79EE87C63462F789E2F9FF6" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Payments to tenants from reserves.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_PaymentsToTenantsFromReserves" xlink:label="loc_good_PaymentsToTenantsFromReserves_23B2E5AAD79EE87C63462F789E2F9FF6" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PaymentsToAcquireRealEstateHeldForInvestment_A9AA5E7181DE06CB13082F789E2F6046_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_PaymentsToAcquireRealEstateHeldForInvestment_A9AA5E7181DE06CB13082F789E2F6046" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xml:lang="en-US">Deposits on future acquisitions</link:label>
    <link:label id="lab_us-gaap_PaymentsToAcquireRealEstateHeldForInvestment_A9AA5E7181DE06CB13082F789E2F6046_label_en-US" xlink:label="lab_us-gaap_PaymentsToAcquireRealEstateHeldForInvestment_A9AA5E7181DE06CB13082F789E2F6046" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Payments to Acquire Real Estate Held-for-investment</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireRealEstateHeldForInvestment" xlink:label="loc_us-gaap_PaymentsToAcquireRealEstateHeldForInvestment_A9AA5E7181DE06CB13082F789E2F6046" xlink:type="locator" />
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    <link:label id="lab_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF_terseLabel_en-US" xlink:label="lab_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Deposits applied against acquisition of real estate investments</link:label>
    <link:label id="lab_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF_label_en-US" xlink:label="lab_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Proceeds From Deposits Applied Against Acquisition Of Real Estate Investments</link:label>
    <link:label id="lab_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF_documentation_en-US" xlink:label="lab_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Proceeds from deposits applied against real estate investments.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments" xlink:label="loc_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF" xlink:to="lab_good_ProceedsFromDepositsAppliedAgainstAcquisitionOfRealEstateInvestments_A2A45162E505317DB60D2F789E2F32FF" xlink:type="arc" />
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivities_7F190C25C79842AE95002F789E30D061_totalLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivities_7F190C25C79842AE95002F789E30D061" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Net cash used in investing activities</link:label>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivities_7F190C25C79842AE95002F789E30D061_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivities_7F190C25C79842AE95002F789E30D061" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Net Cash Provided by (Used in) Investing Activities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7F190C25C79842AE95002F789E30D061" xlink:type="locator" />
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_B5D586282FD1E6359DBC2F789E309215_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_B5D586282FD1E6359DBC2F789E309215" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Cash flows from financing activities:</link:label>
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    <link:label id="lab_us-gaap_ProceedsFromIssuanceOfCommonStock_64CF48A7EDED7437C4572F789E30B758_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromIssuanceOfCommonStock_64CF48A7EDED7437C4572F789E30B758" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Proceeds from issuance of equity</link:label>
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    <link:label id="lab_us-gaap_PaymentsForRepurchaseOfCommonStock_000A4DCCBADF228A7C6A2F789E312BF5_negatedLabel_en-US" xlink:label="lab_us-gaap_PaymentsForRepurchaseOfCommonStock_000A4DCCBADF228A7C6A2F789E312BF5" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Retirement of senior common stock</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertySubjectToOrAvailableForOperatingLeaseDomain" xlink:label="loc_us-gaap_PropertySubjectToOrAvailableForOperatingLeaseDomain_FD5A02CB9F77023F5CB83E4061DBC56B" xlink:type="locator" />
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    <link:label id="lab_us-gaap_OperatingLeasedAssetsLineItems_EF7ECB85D2EC9F844D873E4061DBA157_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasedAssetsLineItems_EF7ECB85D2EC9F844D873E4061DBA157" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Operating Leased Assets [Line Items]</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeasedAssetsLineItems" xlink:label="loc_us-gaap_OperatingLeasedAssetsLineItems_EF7ECB85D2EC9F844D873E4061DBA157" xlink:type="locator" />
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    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_5A1ACCE4080BDF0262263E434911757A_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_5A1ACCE4080BDF0262263E434911757A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Six Months Ending 2019</link:label>
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    <link:label id="lab_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF_terseLabel_en-US" xlink:label="lab_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">April 2019</link:label>
    <link:label id="lab_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF_label_en-US" xlink:label="lab_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Dividend Declared, Period One [Member]</link:label>
    <link:label id="lab_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF_documentation_en-US" xlink:label="lab_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Dividend Declared, Period One [Member]</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_DividendDeclaredPeriodOneMember" xlink:label="loc_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF" xlink:to="lab_good_DividendDeclaredPeriodOneMember_18CFB6257BE3849AE79629C9B40DA0AF" xlink:type="arc" />
    <link:label id="lab_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5_terseLabel_en-US" xlink:label="lab_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">May 2019</link:label>
    <link:label id="lab_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5_label_en-US" xlink:label="lab_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Dividend Declared, Period Two [Member]</link:label>
    <link:label id="lab_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5_documentation_en-US" xlink:label="lab_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Dividend Declared, Period Two [Member]</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_DividendDeclaredPeriodTwoMember" xlink:label="loc_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5" xlink:to="lab_good_DividendDeclaredPeriodTwoMember_BE7F755AD4CDA0E82B6D29C9B40E9FF5" xlink:type="arc" />
    <link:label id="lab_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F_terseLabel_en-US" xlink:label="lab_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">June 2019</link:label>
    <link:label id="lab_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F_label_en-US" xlink:label="lab_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Dividend Declared, Period Three [Member]</link:label>
    <link:label id="lab_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F_documentation_en-US" xlink:label="lab_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Dividend Declared, Period Three [Member]</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_DividendDeclaredPeriodThreeMember" xlink:label="loc_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F" xlink:to="lab_good_DividendDeclaredPeriodThreeMember_E44E936E1880BA3AC4D629C9B40E709F" xlink:type="arc" />
    <link:label id="lab_good_DistributionsPayableToHoldersOfRecordsMonths_E7AF731EB82FD19B991329C9B410070B_terseLabel_en-US" xlink:label="lab_good_DistributionsPayableToHoldersOfRecordsMonths_E7AF731EB82FD19B991329C9B410070B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Payable to the Holders of Record During the Month of:</link:label>
    <link:label id="lab_good_DistributionsPayableToHoldersOfRecordsMonths_E7AF731EB82FD19B991329C9B410070B_label_en-US" xlink:label="lab_good_DistributionsPayableToHoldersOfRecordsMonths_E7AF731EB82FD19B991329C9B410070B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Distributions Payable To Holders Of Records Months</link:label>
    <link:label id="lab_good_DistributionsPayableToHoldersOfRecordsMonths_E7AF731EB82FD19B991329C9B410070B_documentation_en-US" xlink:label="lab_good_DistributionsPayableToHoldersOfRecordsMonths_E7AF731EB82FD19B991329C9B410070B" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Distributions payable to holders of records, months.</link:label>
    <link:loc xlink:href="good-20190630.xsd#good_DistributionsPayableToHoldersOfRecordsMonths" xlink:label="loc_good_DistributionsPayableToHoldersOfRecordsMonths_E7AF731EB82FD19B991329C9B410070B" xlink:type="locator" />
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    <link:label id="lab_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_5723BE78678A8B72CCF229C9B4105A1C_terseLabel_en-US" xlink:label="lab_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_5723BE78678A8B72CCF229C9B4105A1C" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Record Date</link:label>
    <link:label id="lab_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_5723BE78678A8B72CCF229C9B4105A1C_label_en-US" xlink:label="lab_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_5723BE78678A8B72CCF229C9B4105A1C" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Dividends Payable, Date of Record</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DividendsPayableDateOfRecordDayMonthAndYear" xlink:label="loc_us-gaap_DividendsPayableDateOfRecordDayMonthAndYear_5723BE78678A8B72CCF229C9B4105A1C" xlink:type="locator" />
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    <link:label id="lab_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_4E7EA783C5247C40F49429C9B41027F4_terseLabel_en-US" xlink:label="lab_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_4E7EA783C5247C40F49429C9B41027F4" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Payment Date</link:label>
    <link:label id="lab_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_4E7EA783C5247C40F49429C9B41027F4_label_en-US" xlink:label="lab_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_4E7EA783C5247C40F49429C9B41027F4" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Dividends Payable, Date to be Paid</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DividendPayableDateToBePaidDayMonthAndYear" xlink:label="loc_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_4E7EA783C5247C40F49429C9B41027F4" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_4E7EA783C5247C40F49429C9B41027F4" xlink:to="lab_us-gaap_DividendPayableDateToBePaidDayMonthAndYear_4E7EA783C5247C40F49429C9B41027F4" xlink:type="arc" />
    <link:label id="lab_us-gaap_DividendsPayableAmountPerShare_735D07144ACF7DBEBCDD29C9B4119726_terseLabel_en-US" xlink:label="lab_us-gaap_DividendsPayableAmountPerShare_735D07144ACF7DBEBCDD29C9B4119726" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Distribution per share (in dollars per share)</link:label>
    <link:label id="lab_us-gaap_DividendsPayableAmountPerShare_735D07144ACF7DBEBCDD29C9B4119726_label_en-US" xlink:label="lab_us-gaap_DividendsPayableAmountPerShare_735D07144ACF7DBEBCDD29C9B4119726" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Dividends Payable, Amount Per Share</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DividendsPayableAmountPerShare" xlink:label="loc_us-gaap_DividendsPayableAmountPerShare_735D07144ACF7DBEBCDD29C9B4119726" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DividendsPayableAmountPerShare_735D07144ACF7DBEBCDD29C9B4119726" xlink:to="lab_us-gaap_DividendsPayableAmountPerShare_735D07144ACF7DBEBCDD29C9B4119726" xlink:type="arc" />
    <link:label id="lab_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_21FD2E4B750AFEDBB2D742B6A1947381_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_21FD2E4B750AFEDBB2D742B6A1947381" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_21FD2E4B750AFEDBB2D742B6A1947381_label_en-US" xlink:label="lab_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_21FD2E4B750AFEDBB2D742B6A1947381" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_21FD2E4B750AFEDBB2D742B6A1947381" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_21FD2E4B750AFEDBB2D742B6A1947381" xlink:to="lab_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_21FD2E4B750AFEDBB2D742B6A1947381" xlink:type="arc" />
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    <link:label id="lab_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_A2E7A3281B2FD144D30A42B6A1960F0F_label_en-US" xlink:label="lab_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_A2E7A3281B2FD144D30A42B6A1960F0F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]</link:label>
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    <link:label id="lab_us-gaap_EarningsPerShareBasicAbstract_F538CDD39CF0CCD2662842B6A1969EF2_terseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareBasicAbstract_F538CDD39CF0CCD2662842B6A1969EF2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Calculation of basic (loss) earnings per share of common stock:</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareBasicAbstract_F538CDD39CF0CCD2662842B6A1969EF2_label_en-US" xlink:label="lab_us-gaap_EarningsPerShareBasicAbstract_F538CDD39CF0CCD2662842B6A1969EF2" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Earnings Per Share, Basic [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareBasicAbstract" xlink:label="loc_us-gaap_EarningsPerShareBasicAbstract_F538CDD39CF0CCD2662842B6A1969EF2" xlink:type="locator" />
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