Annual report pursuant to Section 13 and 15(d)

Schedule IV - Mortgage Loans on Real Estate (Detail)

v2.4.1.9
Schedule IV - Mortgage Loans on Real Estate (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Mortgage Loans on Real Estate [Line Items]  
Prior Lien $ 0us-gaap_MortgageLoansOnRealEstatePriorLiens1
Face Amount of Mortgage 642,500,000us-gaap_MortgageLoansOnRealEstateFaceAmountOfMortgages
Carrying Amount of Mortgage 5,600,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
Principal Amount of Loans Subject to Delinquent Principal or Interest 0us-gaap_MortgageLoansOnRealEstatePrincipalAmountOfDelinquentLoans
Build To Suit Healthcare Facility [Member] | Phoenix,Arizona [Member] | Second Mortgage [Member]  
Mortgage Loans on Real Estate [Line Items]  
Final Maturity Date Jul. 31, 2016
Periodic Payment Term 9.0% interest, paid currently in cash on the loan during construction and through maturity. Exit fee upon maturity of the loan in an amount sufficient to earn a 22% internal rate of return.
Prior Lien 0us-gaap_MortgageLoansOnRealEstatePriorLiens1
/ us-gaap_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis
= us-gaap_SecondMortgageMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= good_BuildToSuitHealthcareFacilityMember
/ us-gaap_StatementGeographicalAxis
= good_PhoenixArizonaMember
Face Amount of Mortgage 5,600,000us-gaap_MortgageLoansOnRealEstateFaceAmountOfMortgages
/ us-gaap_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis
= us-gaap_SecondMortgageMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= good_BuildToSuitHealthcareFacilityMember
/ us-gaap_StatementGeographicalAxis
= good_PhoenixArizonaMember
Carrying Amount of Mortgage 5,600,000us-gaap_MortgageLoansOnRealEstateCarryingAmountOfMortgages
/ us-gaap_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis
= us-gaap_SecondMortgageMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= good_BuildToSuitHealthcareFacilityMember
/ us-gaap_StatementGeographicalAxis
= good_PhoenixArizonaMember
Principal Amount of Loans Subject to Delinquent Principal or Interest $ 0us-gaap_MortgageLoansOnRealEstatePrincipalAmountOfDelinquentLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis
= us-gaap_SecondMortgageMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= good_BuildToSuitHealthcareFacilityMember
/ us-gaap_StatementGeographicalAxis
= good_PhoenixArizonaMember
Loan bearing interest, terms 9% Current Interest, 22% internal rate of return on exit
Interest of loan 9.00%us-gaap_MortgageLoansOnRealEstateInterestRate
/ us-gaap_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis
= us-gaap_SecondMortgageMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= good_BuildToSuitHealthcareFacilityMember
/ us-gaap_StatementGeographicalAxis
= good_PhoenixArizonaMember
Internal rate of return on exit 22.00%good_MortgageLoanTargetInternalRateOfReturn
/ us-gaap_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis
= us-gaap_SecondMortgageMember
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= good_BuildToSuitHealthcareFacilityMember
/ us-gaap_StatementGeographicalAxis
= good_PhoenixArizonaMember