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Leases (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Leases [Abstract] |  |
ROU Asset Impairment | $ 2.6 | $ 1.8

X
- Definition ROU Asset Impairment + References No definition available. + Details
Name: | colb_ROUAssetImpairment
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_LeasesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration