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v3.21.2

Intangible Assets, Goodwill and Other (Details) - Narrative | 9 Months Ended
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Sep. 30, 2021
Core Deposits [Member] |
Goodwill and Intangible Assets [Line Items] |
Estimated life of CDI, in years | 10 years

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- Definition Goodwill and Intangible Assets [Line Items] + References No definition available. + Details
Name: | colb_GoodwillAndIntangibleAssetsLineItems
Namespace Prefix: | colb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CoreDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |