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v3.19.1

Junior subordinated debt (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2017 | Nov. 01, 2017
Junior subordinated debentures [Line Items] |  |  |  |
Repayments of junior subordinated debt | $ 0 | $ 8,248 | $ 6,200 |
Pacific Continental [Member] |  |  |  |
Junior subordinated debentures [Line Items] |  |  |  |
Business Combination, Purchase Price Allocation, Junior Subordinated Debentures |  |  |  | $ 14,400

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- Definition Business Combination, Purchase Price Allocation, Junior Subordinated Debentures + References No definition available. + Details
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- Definition [Line Items] for junior subordinated debentures [Table] + References No definition available. + Details
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Namespace Prefix: | colb_
Data Type: | xbrli:stringItemType
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- Definition Repayments of junior subordinated debt + References No definition available. + Details
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Namespace Prefix: | colb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |