Document And Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2015	Dec. 02, 2015	Mar. 31, 2015
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		3,619,148
Entity Public Float			$ 25,577,347
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, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY