Capital Requirements and Regulatory Restrictions (Tables)

12 Months Ended

Dec. 31, 2017

Regulatory Capital Requirements [Abstract]

Schedule of Capital Amounts and Ratios

The Company’s and the Bank’s actual and required capital amounts and ratios are as follows:

					Capital				Requirement to be
	Actual				Requirements				Well-Capitalized
(In thousands)	Amount		Ratio		Amount		Ratio		Amount		Ratio
At December 31, 2017
Total capital (to risk-weighted assets)
Cass Information Systems, Inc.	$	234,389	22.53	%	$	83,233	8.00	%	$	N/A	N/A	%
Cass Commercial Bank		122,440	17.01			57,568	8.00			71,960	10.00
Common Equity Tier I Capital (to risk-weighted assets)
Cass Information Systems, Inc.		224,184	21.55			46,819	4.50			N/A	N/A
Cass Commercial Bank		114,603	15.93			32,382	4.50			46,774	6.50
Tier I capital (to risk-weighted assets)
Cass Information Systems, Inc.		224,184	21.55			62,425	6.00			N/A	N/A
Cass Commercial Bank		114,603	15.93			43,176	6.00			57,568	8.00
Tier I capital (to average assets)
Cass Information Systems, Inc.		224,184	13.87			64,649	4.00			N/A	N/A
Cass Commercial Bank		114,603	14.99			30,581	4.00			38,227	5.00
At December 31, 2016
Total capital (to risk-weighted assets)
Cass Information Systems, Inc.	$	219,747	22.75	%	$	77,272	8.00	%	$	N/A	N/A	%
Cass Commercial Bank		110,576	16.72			52,898	8.00			66,123	10.00
Common Equity Tier I Capital (to risk-weighted assets)
Cass Information Systems, Inc.		209,572	21.70			43,466	4.50			N/A	N/A
Cass Commercial Bank		102,769	15.54			29,755	4.50			42,980	6.50
Tier I capital (to risk-weighted assets)
Cass Information Systems, Inc.		209,572	21.70			57,954	6.00			N/A	N/A
Cass Commercial Bank		102,769	15.54			39,674	6.00			52,898	8.00
Tier I capital (to average assets)
Cass Information Systems, Inc.		209,572	13.83			60,620	4.00			N/A	N/A
Cass Commercial Bank		102,769	13.98			29,409	4.00			36,761	5.00