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Document And Entity Information (USD $)
 12 Months Ended
Sep. 30, 2011
Jan. 09, 2012
Mar. 31, 2011
Document and Entity Information [Abstract]      
Entity Registrant Name CSP INC /MA/    
Document Type 10-K    
Current Fiscal Year End Date --09-30    
Entity Common Stock, Shares Outstanding   3,396,154  
Entity Public Float     $ 17,938,843
Amendment Flag false    
Entity Central Index Key 0000356037    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Smaller Reporting Company    
Entity Well-known Seasoned Issuer No    
Document Period End Date Sep. 30, 2011    
Document Fiscal Year Focus 2011    
Document Fiscal Period Focus FY