Common Stock and Earnings per Share (Narrative) (Details)	12 Months Ended
Dec. 31, 2013
Common Stock and Earnings per Share [Abstract]
Stock dividend, percent	10.00%

The percentage rate used to calculate dividend payments on common stock.

No definition available.

Name:	cass_CommonStockDividendRatePercentage
Namespace Prefix:	cass_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration