Goodwill and Other Intangible Assets (Schedule of Estimated Annual Amortization Expense for Next Five Years) (Details) (USD $) In Thousands	6 Months Ended
Jun. 30, 2011
Goodwill and Other Intangible Assets
2011	$ 2,870
2012	2,331
2013	1,795
2014	1,315
2015	$ 967

Goodwill and Other Intangible Assets [Abstract]

Name:	cbsh_GoodwillAndOtherIntangibleAssetsAbstract
Namespace Prefix:	cbsh
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of amortization expense expected to be recognized during the fifth twelve-month period following the balance sheet date.