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Covered Assets and FDIC Loss-sharing Asset (Narrative) (Details) $ in Thousands | 3 Months Ended
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Mar. 31, 2016 USD ($)
Covered Assets And FDIC Loss Sharing Asset [Line Items] |
Amount of Estimated Clawback Liability | $ 5,418
Payment Of Clawback If Losses Less Than Stated Levels, Period After Acquisition | 10 years 45 days
Federal deposit insurance corporation loss-sharing indemnified assets | $ 4,600
Federal deposit insurance corporation loss-sharing indemnified assets receivable | $ 1,400
Maximum [Member] |
Covered Assets And FDIC Loss Sharing Asset [Line Items] |
Loss Sharing Agreement Effective Years | 10 years
Loss Recovery Provision Effective Years | 10 years
Minimum [Member] |
Covered Assets And FDIC Loss Sharing Asset [Line Items] |
Loss Sharing Agreement Effective Years | 5 years
Loss Recovery Provision Effective Years | 8 years
Covered Loans [Member] |
Covered Assets And FDIC Loss Sharing Asset [Line Items] |
Percentage of loss shared by FDIC | 80.00%
FDIC Percentage Of Loss Recoveries | 80.00%
Percentage of loss shared by FDIC When Loss Share Thresholds Met | 95.00%
Percentage Of Loss Recoveries Shared By FDIC When Loss Share Thresholds Met | 95.00%

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- Definition Covered Assets And FDIC Loss Sharing Asset [Line Items] + References No definition available. + Details
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Data Type: | xbrli:stringItemType
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- Definition FDIC Percentage Of Loss Recoveries + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Definition Federal deposit insurance corporation loss-sharing indemnified assets + References No definition available. + Details
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- Definition Federal deposit insurance corporation loss-sharing indemnified assets receivable + References No definition available. + Details
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- Definition Loss Recovery Provision Effective Years + References No definition available. + Details
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Period Type: | duration

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- Definition Loss Sharing Agreement Effective Years + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition Payment Of Clawback If Losses Less Than Stated Levels, Period After Acquisition + References No definition available. + Details
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Data Type: | us-types:durationStringItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage Of Loss Recoveries Shared By FDIC When Loss Share Thresholds Met + References No definition available. + Details
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Namespace Prefix: | colb_
Data Type: | num:percentItemType
Balance Type: | na
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- Definition Percentage of loss shared by FDIC + References No definition available. + Details
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- Definition Percentage of loss shared by FDIC When Loss Share Thresholds Met + References No definition available. + Details
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Namespace Prefix: | colb_
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Balance Type: | na
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | colb_LoansByMajorCategoryAxis=colb_CoveredLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |