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Residential Mortgage Servicing Rights (Schedule Of Information Relates To Serviced Loan Portfolio) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Transfers and Servicing [Abstract] |  |  |
Balance of loans serviced for others | $ 8,175,664 | $ 13,020,189 | $ 12,755,671
MSR as a percentage of serviced loans | 1.34% | 1.42% | 0.97%

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- Definition Balance of loans serviced for others. + References No definition available. + Details
Name: | colb_BalanceOfLoansServicedForOthers
Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Mortgage servicing rights, percentage of serviced loans + References No definition available. + Details
Name: | colb_MortgageServicingRightsPercentageOfServicedLoans
Namespace Prefix: | colb_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

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