Quarterly report pursuant to Section 13 or 15(d)

Mortgage Notes Payable and Line of Credit - Summary of Long-Term Mortgage (Detail)

v2.4.1.9
Mortgage Notes Payable and Line of Credit - Summary of Long-Term Mortgage (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Debt Instrument [Line Items]    
Debt Issued $ 14,573us-gaap_MortgageLoansOnRealEstateNewMortgageLoans $ 6,330us-gaap_MortgageLoansOnRealEstateNewMortgageLoans
PNC Bank, NA [Member] | Maturity Date One [Member]    
Debt Instrument [Line Items]    
Date of Issuance Mar. 06, 2015  
Issuing Bank PNC Bank, NA  
Debt Issued $ 14,573us-gaap_MortgageLoansOnRealEstateNewMortgageLoans
/ us-gaap_DebtInstrumentAxis
= good_MaturityDateOneMember
/ us-gaap_LineOfCreditFacilityAxis
= good_PncBankNaMember
 
Interest Rate 3.86%us-gaap_MortgageLoansOnRealEstateInterestRate
/ us-gaap_DebtInstrumentAxis
= good_MaturityDateOneMember
/ us-gaap_LineOfCreditFacilityAxis
= good_PncBankNaMember
 
Maturity Date Apr. 01, 2025