Document And Entity Information - shares	6 Months Ended
	Mar. 31, 2021	May 05, 2021
Document and Entity Information
Entity Registrant Name	CSP INC /MA/
Document Type	10-Q
Current Fiscal Year End Date	--09-30
Entity Common Stock, Shares Outstanding		4,393,966
Amendment Flag	false
Entity Central Index Key	0000356037
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	CSPI
Security Exchange Name	NASDAQ