Parent Company Condensed Financial Statements (Condensed Statements Of Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest and dividends on investment securities	$ 240,187	$ 214,689	$ 207,184
Salaries and employee benefits	468,194	448,321	427,310
Data processing fees paid to affiliates	85,978	80,998	79,589
Community Service	2,445	34,377	3,906
Other	64,304	63,366	59,499
Total non-interest expense	737,821	744,343	689,229
Income tax expense (benefit)	105,949	110,506	124,151
NET INCOME ATTRIBUTABLE TO COMMERCE BANCSHARES, INC.	433,542	319,383	275,391
Commerce Bancshares, Inc. (Parent) [Member]
Dividends received from consolidated subsidiary banks	200,000	160,002	160,002
Earnings of consolidated subsidiaries, net of dividends	233,785	147,678	118,704
Interest and dividends on investment securities	10,698	2,099	2,364
Management fees charged subsidiaries	37,688	30,431	30,965
Investment securities gains (losses)	(4,581)	41,717	1,880
Net interest income on advances and note to subsidiaries	1,299	514	21
Other	2,390	3,346	2,720
Total income	481,279	385,787	316,656
Salaries and employee benefits	33,588	33,714	29,116
Professional fees	2,383	2,036	1,951
Data processing fees paid to affiliates	3,341	3,512	3,226
Community Service	152	32,093	1,620
Other	10,729	10,671	9,849
Total non-interest expense	50,193	82,026	45,762
Income tax expense (benefit)	(2,456)	(15,622)	(4,497)
NET INCOME ATTRIBUTABLE TO COMMERCE BANCSHARES, INC.	$ 433,542	$ 319,383	$ 275,391