Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Summary of Outstanding Note Issued to Employee for Exercise of Stock Options (Detail)

v2.4.1.9
Stockholders' Equity - Summary of Outstanding Note Issued to Employee for Exercise of Stock Options (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Debt Conversion [Line Items]    
Outstanding Balance of Employee Loan $ 375us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock $ 375us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock
Note Outstanding One [Member]    
Debt Conversion [Line Items]    
Date Issued 2006-11  
Outstanding Balance of Employee Loan $ 375us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock
/ us-gaap_DebtInstrumentAxis
= good_NoteOutstandingOneMember
$ 375us-gaap_ReceivableFromShareholdersOrAffiliatesForIssuanceOfCapitalStock
/ us-gaap_DebtInstrumentAxis
= good_NoteOutstandingOneMember
Maturity Date of Note 2015-11  
Interest Rate on Note 8.15%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= good_NoteOutstandingOneMember