DOCUMENT AND ENTITY INFORMATION	9 Months Ended
	Sep. 30, 2012	Oct. 26, 2012
Entity Registrant Name	CASS INFORMATION SYSTEMS INC
Entity Central Index Key	0000708781
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Trading Symbol	cass
Entity Common Stock, Shares Outstanding		10,397,885
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2012
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2012