Quarterly report pursuant to Section 13 or 15(d)

Related-Party Transactions - Additional Information (Detail)

v2.4.1.9
Related-Party Transactions - Additional Information (Detail) (USD $)
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Related Party Transaction [Line Items]      
Due to Adviser and Administrator $ 1,721,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent [1]   $ 916,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent [1]
Annual base management fee, in percentage of stockholders' equity, in excess of recorded value of preferred stock 2.00%good_AnnualBaseManagementFeeInPercentageOfStockholdersEquityInExcessOfRecordedValueOfPreferredStock    
Base management fee 852,000good_BaseManagementFee [1] 625,000good_BaseManagementFee [1]  
Pre-incentive quarterly fee FFO in percentage of common stockholders' equity that will reward the Adviser 1.75%good_IncentiveFeePerAdvisoryAgreement    
Pre-incentive annual fee FFO in percentage of common stockholders' equity that will reward the Adviser 7.00%good_AnnualizedIncentiveFeePerAdvisoryAgreement    
Amount to be paid to Adviser in percentage of pre-incentive fee condition one 100.00%good_AmountToBePaidToAdviserInPercentageOfPreIncentiveFeeConditionOne    
Pre-incentive fee in percentage of common stockholders' equity that awards Adviser hundred percent of amount of pre-incentive fee, maximum percentage 2.1875%good_PreIncentiveFeeInPercentageOfCommonStockholdersEquityThatAwardsAdviserHundredPercentOfAmountOfPreIncentiveFeeMaximumPercentage    
Amount to be paid to Adviser in percentage of pre-incentive fee condition two 20.00%good_AmountToBePaidToAdviserInPercentageOfPreIncentiveFeeConditionTwo    
Pre-incentive fee in percentage of common stockholders' equity that awards the Adviser 20% of the amount of the pre-incentive fee, minimum percentage 2.1875%good_PreIncentiveFeeInPercentageOfCommonStockholdersEquityThatAwardsAdviserTwentyPercentOfAmountOfPreIncentiveFeeMinimumPercentage    
Incentive fee 1,673,000good_IncentiveFee [1] 1,240,000good_IncentiveFee [1]  
Credits related to unconditional and irrevocable voluntary waivers issued by the Adviser 1,185,000good_CreditToIncentiveFee [1] 1,205,000good_CreditToIncentiveFee [1]  
Related-party transactions incentive fee, net 500,000good_RelatedPartyTransactionsIncentiveFeeNet 40,000good_RelatedPartyTransactionsIncentiveFeeNet  
Administration fee 362,000good_AdministrationFee [1] 492,000good_AdministrationFee [1]  
Dealer manager fee in percentage of gross proceeds of shares of Senior Common Stock sold 7.00%good_DealerManagerFeeInPercentageOfGrossProceedsOfSharesOfSeniorCommonStockSold    
Sales commission fee in percentage of gross proceeds of shares of Senior Common Stock sold 3.00%good_SalesCommissionFeeInPercentageOfGrossProceedsOfSharesOfSeniorCommonStockSold    
Agreement termination date Aug. 31, 2015    
Fees paid 38,000good_PaymentOfFinancingFee 0good_PaymentOfFinancingFee  
Total secured mortgages subject to financing fee 14,600,000us-gaap_SecuredDebt    
Financing fee on secured mortgages percentage 0.26%good_SecuredMortgagesFinancingFeePercent    
Minimum [Member]      
Related Party Transaction [Line Items]      
Percentage of the amount of the mortgage 0.15%good_PercentageOfFinancingFeeToAmountOfMortgage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember 		   
Maximum [Member]      
Related Party Transaction [Line Items]      
Percentage of the amount of the mortgage 1.00%good_PercentageOfFinancingFeeToAmountOfMortgage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		   
Dealer Manager [Member]      
Related Party Transaction [Line Items]      
Payments made to the Dealer Manager pursuant to Dealer Manager Agreement 300,000us-gaap_PaymentsForAdvanceToAffiliate
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= good_DealerManagerMember 		40,000us-gaap_PaymentsForAdvanceToAffiliate
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= good_DealerManagerMember 		 
Agreement termination date Mar. 28, 2015    
Wrote-off of deferred offering costs $ 100,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= good_DealerManagerMember 		   
[1] Refer to Note 2 "Related-Party Transactions"