Quarterly report pursuant to Section 13 or 15(d)

Real Estate and Intangible Assets - Schedule of Revenue and Earnings Recognized on Properties Acquired (Detail)

v2.4.1.9
Real Estate and Intangible Assets - Schedule of Revenue and Earnings Recognized on Properties Acquired (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Business Acquisition [Line Items]    
Rental Revenue $ 193good_OperatingLeasesIncomeStatementLeaseRevenueFromAcquiredProperties $ 14good_OperatingLeasesIncomeStatementLeaseRevenueFromAcquiredProperties
Earnings 55good_NetIncomeLossFromAcquiredProperties 9good_NetIncomeLossFromAcquiredProperties
Richardson, TX [Member]    
Business Acquisition [Line Items]    
Acquisition Date Mar. 06, 2015  
Rental Revenue 182good_OperatingLeasesIncomeStatementLeaseRevenueFromAcquiredProperties
/ us-gaap_BusinessAcquisitionAxis
= good_RichardsonTxMember
 
Earnings 51good_NetIncomeLossFromAcquiredProperties
/ us-gaap_BusinessAcquisitionAxis
= good_RichardsonTxMember
 
Birmingham, AL [Member]    
Business Acquisition [Line Items]    
Acquisition Date Mar. 20, 2015  
Rental Revenue 11good_OperatingLeasesIncomeStatementLeaseRevenueFromAcquiredProperties
/ us-gaap_BusinessAcquisitionAxis
= good_BirminghamAlMember
 
Earnings 4good_NetIncomeLossFromAcquiredProperties
/ us-gaap_BusinessAcquisitionAxis
= good_BirminghamAlMember
 
Allen, TX [Member]    
Business Acquisition [Line Items]    
Acquisition Date   Mar. 27, 2014
Rental Revenue   8good_OperatingLeasesIncomeStatementLeaseRevenueFromAcquiredProperties
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTXMember
Earnings   5good_NetIncomeLossFromAcquiredProperties
/ us-gaap_BusinessAcquisitionAxis
= good_AllenTXMember
Colleyville, TX [Member]    
Business Acquisition [Line Items]    
Acquisition Date   Mar. 27, 2014
Rental Revenue   6good_OperatingLeasesIncomeStatementLeaseRevenueFromAcquiredProperties
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilleTxMember
Earnings   $ 4good_NetIncomeLossFromAcquiredProperties
/ us-gaap_BusinessAcquisitionAxis
= good_ColleyvilleTxMember