Cover Page - shares	3 Months Ended
	Mar. 31, 2022	Apr. 22, 2022
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2022
Document Transition Report	false
Entity File Number	000-20827
Entity Registrant Name	CASS INFORMATION SYSTEMS, INC.
Entity Incorporation, State or Country Code	MO
Entity Tax Identification Number	43-1265338
Entity Address, Address Line One	12444 Powerscourt Drive
Entity Address, Address Line Two	Suite 550
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63131
City Area Code	314
Local Phone Number	506-5500
Title of 12(b) Security	Common stock, par value $.50
Trading Symbol	CASS
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		13,652,849
Entity Central Index Key	0000708781
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1