Goodwill And Other Intangible Assets (Narrative) (Details) (USD $) In Thousands, unless otherwise specified
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12 Months Ended |
Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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Finite-Lived Intangible Assets [Line Items] |
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Impairment of goodwill |
$ 0us-gaap_GoodwillImpairmentLoss |
$ 0us-gaap_GoodwillImpairmentLoss |
$ 0us-gaap_GoodwillImpairmentLoss |
Aggregate amortization expense for intangible assets |
2,100us-gaap_AmortizationOfIntangibleAssets |
2,200us-gaap_AmortizationOfIntangibleAssets |
2,500us-gaap_AmortizationOfIntangibleAssets |
Goodwill [Member] |
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Finite-Lived Intangible Assets [Line Items] |
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Aggregate amortization expense for intangible assets |
0us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_GoodwillMember |
0us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_GoodwillMember |
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Goodwill and Intangible Assets Acquired |
0cbsh_GoodwillandIntangibleAssetsAcquired / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_GoodwillMember |
13,336cbsh_GoodwillandIntangibleAssetsAcquired / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_GoodwillMember |
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Core Deposits [Member] |
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Finite-Lived Intangible Assets [Line Items] |
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Aggregate amortization expense for intangible assets |
1,917us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |
1,889us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |
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Goodwill and Intangible Assets Acquired |
0cbsh_GoodwillandIntangibleAssetsAcquired / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |
5,550cbsh_GoodwillandIntangibleAssetsAcquired / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |
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Mortgage Servicing Rights [Member] |
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Finite-Lived Intangible Assets [Line Items] |
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Recognized temporary impairment |
97us-gaap_GoodwillAndIntangibleAssetImpairment / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = cbsh_MortgageServicingRightsMember |
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Aggregate amortization expense for intangible assets |
151us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = cbsh_MortgageServicingRightsMember |
300us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = cbsh_MortgageServicingRightsMember |
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Goodwill and Intangible Assets Acquired |
$ 0cbsh_GoodwillandIntangibleAssetsAcquired / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = cbsh_MortgageServicingRightsMember |
$ 0cbsh_GoodwillandIntangibleAssetsAcquired / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = cbsh_MortgageServicingRightsMember |
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