Document And Entity Information - shares	3 Months Ended
	Dec. 31, 2021	Feb. 09, 2022
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2021
Entity File Number	0-10843
Entity Registrant Name	CSP Inc
Entity Incorporation, State or Country Code	MA
Entity Tax Identification Number	04-2441294
Entity Address, Address Line One	175 Cabot Street
Entity Address, Address Line Two	Suite 210
Entity Address, City or Town	Lowell
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01854
City Area Code	978
Local Phone Number	954-5038
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		4,529,810
Entity Central Index Key	0000356037
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Amendment Flag	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	CSPI
Security Exchange Name	NASDAQ