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Residential Mortgage Servicing Rights (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Transfers and Servicing [Abstract] |  |  |
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset | $ 33,400 | $ 37,400 | $ 36,800
Sale of MSR assets | 57,305 | $ 0 | $ 0
Residential Mortgage Loans Serviced for Others, Disposal | $ 4,300,000 |  |

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- Definition Residential Mortgage Loans Serviced for Others disposed of during the period. + References No definition available. + Details
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Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amount of contractually specified servicing fee, late fee, and ancillary fee recognized as income for servicing asset and servicing liability. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 860 -SubTopic 50 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481229/860-50-50-2 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Decrease in servicing assets subsequently measured at fair value resulting from conveyance of servicing rights to unrelated parties. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 860 -SubTopic 50 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481229/860-50-50-3 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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