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v3.20.1

Fair Value Accounting and Measurement (Quantitative Information About Level 3 Fair Value Measurements) (Details) - Fair Value, Nonrecurring [Member] $ in Thousands | Mar. 31, 2020 USD ($) | Mar. 31, 2019 USD ($)
--- | --- | ---
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Collateral dependent loans, Fair Value | $ 3,043 | $ 3,840
Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Collateral dependent loans, Fair Value | $ 3,043 | $ 3,840
Valuation, Market Approach [Member] | Minimum [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Collateral dependent loans, Measurement Input | 0.0000 | 0.0000
Valuation, Market Approach [Member] | Maximum [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Collateral dependent loans, Measurement Input | 1.0000 | 1.0000
Valuation, Market Approach [Member] | Weighted Average [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31) |  |
Collateral dependent loans, Measurement Input | 0.5978 | 0.4453

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- Definition Collateral dependent loans, Fair Value + 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 Collateral dependent loans, Measurement Input + References No definition available. + Details
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Namespace Prefix: | colb_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
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- Details
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- Details
Name: | us-gaap_ValuationTechniqueAxis=us-gaap_MarketApproachValuationTechniqueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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- Details
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Period Type: |

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