Common Stock (Details) (USD $) In Thousands, except Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Net income attributable to Commerce Bancshares, Inc.	$ 69,034	$ 59,734	$ 129,487	$ 103,904
Basic income per common share	$ 0.80	$ 0.69	$ 1.49	$ 1.19
Diluted income per common share	$ 0.79	$ 0.68	$ 1.48	$ 1.18
Diluted income per common share computations in unexercised stock options and stock appreciation rights				1,700,000
Basic Income Per Common Share [Member]
Net income attributable to Commerce Bancshares, Inc.	69,034	59,734	129,487	103,904
Less income allocated to nonvested restricted stockholders	501	331	905	565
Net income available to common stockholders	68,533	59,403	128,582	103,339
Distributed income	19,909	19,505	39,816	38,992
Undistributed income	48,624	39,898	88,766	64,347
Weighted average common shares outstanding	86,539,000	87,139,000	86,504,000	87,079,000
Distributed income per share	$ 0.23	$ 0.23	$ 0.46	$ 0.45
Undistributed income per share	$ 0.57	$ 0.46	$ 1.03	$ 0.74
Basic income per common share	$ 0.80	$ 0.69	$ 1.49	$ 1.19
Diluted Income Per Common Share [Member]
Net income attributable to Commerce Bancshares, Inc.	69,034	59,734	129,487	103,904
Less income allocated to nonvested restricted stockholders	499	329	902	563
Net income available to common stockholders	68,535	59,405	128,585	103,341
Distributed income	19,909	19,505	39,816	38,992
Undistributed income	$ 48,626	$ 39,900	$ 88,769	$ 64,349
Weighted average common shares outstanding	86,539,000	87,139,000	86,504,000	87,079,000
Net effect of the assumed exercise of stock-based awards - based on the treasury stock method using the average market price for the respective periods	388,000	415,000	378,000	444,000
Weighted average diluted common shares outstanding	86,927,000	87,554,000	86,882,000	87,523,000
Distributed income per share	$ 0.23	$ 0.23	$ 0.46	$ 0.45
Undistributed income per share	$ 0.56	$ 0.45	$ 1.02	$ 0.73
Diluted income per common share	$ 0.79	$ 0.68	$ 1.48	$ 1.18

Total cash dividends paid during the period to common shareholders, less dividends paid on unvested restricted stock, on a per share basis.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.

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