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Document and Entity Information (USD $)
 12 Months Ended
Dec. 31, 2014
Feb. 10, 2015
Jun. 30, 2014
Document and Entity Information      
Entity Registrant Name FRANKLIN STREET PROPERTIES CORP /MA/    
Entity Central Index Key 0001031316    
Document Type 10-K    
Document Period End Date Dec. 31, 2014    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 1,133,357,746dei_EntityPublicFloat
Entity Common Stock, Shares Outstanding   100,187,405dei_EntityCommonStockSharesOutstanding  
Document Fiscal Year Focus 2014    
Document Fiscal Period Focus FY