Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Additional Information (Detail)

v2.4.1.9
Stockholders' Equity - Additional Information (Detail) (USD $)
 0 Months Ended 1 Months Ended 12 Months Ended
Dec. 31, 2014
Jun. 06, 2014
Mar. 31, 2011
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Class of Stock [Line Items]            
Capital gains       0.00%good_CapitalGainDistributions 0.00%good_CapitalGainDistributions 0.00%good_CapitalGainDistributions
Common stock, shares issued 19,589,606us-gaap_CommonStockSharesIssued     19,589,606us-gaap_CommonStockSharesIssued 15,662,414us-gaap_CommonStockSharesIssued  
Gross proceeds of initial public offering   $ 27,400,000us-gaap_ProceedsFromIssuanceInitialPublicOffering        
Net proceeds of initial public offering   26,000,000good_NetProceedsFromIssuanceInitialPublicOffering        
Common stock, par value $ 0.001us-gaap_CommonStockParOrStatedValuePerShare     $ 0.001us-gaap_CommonStockParOrStatedValuePerShare $ 0.001us-gaap_CommonStockParOrStatedValuePerShare  
Shares intended to be offered pursuant to primary offering     3,000,000good_SharesIntendedToBeOfferedPursuantToPrimaryOffering      
Shares intended to be offered pursuant to senior common distribution reinvestment plan     500,000us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan      
Shares of senior common stock sold in ongoing offering 738,942good_SharesOfSeniorCommonStockSoldInThisOngoingOffering          
Senior common stock ongoing offering, gross proceeds       73,931,000us-gaap_ProceedsFromIssuanceOfCommonStock 88,121,000us-gaap_ProceedsFromIssuanceOfCommonStock 4,191,000us-gaap_ProceedsFromIssuanceOfCommonStock
Shares of senior common stock issued 809,411good_SeniorCommonStockSharesIssued     809,411good_SeniorCommonStockSharesIssued 374,484good_SeniorCommonStockSharesIssued  
Cantor Fitzgerald & Co [Member]            
Class of Stock [Line Items]            
Maximum aggregate sales price of shares to be issued under open market sale agreement 100,000,000good_MaximumAggregateSalesPriceOfSharesToBeIssuedUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_CantorFitzgeraldAndCompanyMember 		    100,000,000good_MaximumAggregateSalesPriceOfSharesToBeIssuedUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_CantorFitzgeraldAndCompanyMember 		   
Percentage of compensation of gross proceeds on sale of common stock       2.00%good_CompensationPercentageOfGrossProceedsFromSaleOfCommonShares
/ dei_LegalEntityAxis
= good_CantorFitzgeraldAndCompanyMember 		   
Number of shares sold under open market sale agreement 1,900,000good_NumberOfSharesSoldUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_CantorFitzgeraldAndCompanyMember 		    1,900,000good_NumberOfSharesSoldUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_CantorFitzgeraldAndCompanyMember 		   
Net proceeds of shares sold under open market sale agreement       32,000,000good_NetProceedsOfSharesSoldUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_CantorFitzgeraldAndCompanyMember 		   
Maximum remaining capacity to sell common stock under open market sale agreement 67,500,000good_MaximumRemainingCapacityToSellCommonStockUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_CantorFitzgeraldAndCompanyMember 		    67,500,000good_MaximumRemainingCapacityToSellCommonStockUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_CantorFitzgeraldAndCompanyMember 		   
Jefferies LLC [Member]            
Class of Stock [Line Items]            
Maximum aggregate sales price of shares to be issued under open market sale agreement 25,000,000good_MaximumAggregateSalesPriceOfSharesToBeIssuedUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_JefferiesMember 		    25,000,000good_MaximumAggregateSalesPriceOfSharesToBeIssuedUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_JefferiesMember 		   
Net proceeds under ATM program       7,600,000us-gaap_ProceedsFromIssuanceOrSaleOfEquity
/ dei_LegalEntityAxis
= good_JefferiesMember 		   
Gross proceeds of shares sold under open market sale agreement       21,800,000good_GrossProceedsOfSharesSoldUnderOpenMarketSaleAgreement
/ dei_LegalEntityAxis
= good_JefferiesMember 		   
Senior Common Stock [Member]            
Class of Stock [Line Items]            
Common stock, shares issued     3,500,000us-gaap_CommonStockSharesIssued
/ us-gaap_StatementClassOfStockAxis
= good_SeniorCommonStockMember 		     
Common stock, par value     0.001us-gaap_CommonStockParOrStatedValuePerShare
/ us-gaap_StatementClassOfStockAxis
= good_SeniorCommonStockMember 		     
Common stock shares issued, selling price     15.00good_CommonStockSharesIssuedSellingPrice
/ us-gaap_StatementClassOfStockAxis
= good_SeniorCommonStockMember 		     
Senior common stock ongoing offering, gross proceeds $ 11,100,000us-gaap_ProceedsFromIssuanceOfCommonStock
/ us-gaap_StatementClassOfStockAxis
= good_SeniorCommonStockMember 		         
Distribution Reinvestment Plan [Member]            
Class of Stock [Line Items]            
Shares of senior common stock issued 24,315good_SeniorCommonStockSharesIssued
/ us-gaap_StatementClassOfStockAxis
= good_DistributionReinvestmentPlanMember 		    24,315good_SeniorCommonStockSharesIssued
/ us-gaap_StatementClassOfStockAxis
= good_DistributionReinvestmentPlanMember 		   
Public Offering [Member]            
Class of Stock [Line Items]            
Common stock, shares issued   1,610,000us-gaap_CommonStockSharesIssued
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember 		       
Public offering price per share   $ 17.00us-gaap_SaleOfStockPricePerShare
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember